Fat Bass Tone
Class D typically refers to digital 'ICEpower’ power sections manufactured by stereo manufacturer Bang and Olufsen that are in just about every bass amp on the market.
They have been pretty revolutionary in allowing amps to get much lighter in a hurry as compared to the transistor based designs that they supplanted. Most amps made post 2006 has used ICEpower.
With Class G Jad Freer is trying differentiate themselves from those ICE modules. They are making the power sections themselves and they are transistor based rather than digital, but done so in a way that produces a light weight and compact power section.
Though arguable not as light weight or as compact as digital, it bridges the gap between how the older transistor (think GK, SWR and Eden) amps sounded, but in a size and weight we don't mind hauling around to gigs
Yes the purchase of a Bullhead 3K Bass Amp includes the rack ears.
The 5 string Sadowsky MetroExpress Basses typically weigh around 9lbs.
While string spacing matters as the size of the bridge changes, the difference in weight is roughly 5 ounces on a 4 string Hipshot A Style Bass Bridge.
The Sire V7 basses (and possibly other 5 string basses from Sire) use a mounting pattern that is the same as Fender has used on some Squire 5 strings.
Here is what the screw mounting pattern looks like modeled on a Hipshot Kickass Mounting Style 2:

The above measurements that are highlighted pink correspond to the center to center measurements from one screw hole to the adjacent screw hole.
.606" = 15.4mm
.706" = 17.9mm
Hipshot's Kickass Bridge with Mounting Pattern 2 is a great choice for retrofitting on a Sire V7 Bass. The bridge has moveable saddles to dial in string spacing. It is a high mass bridge that is also= attractive. It does not support string through body mounting.
The Hipshot A Style, B Style, Vintage and Kickass bridges can all be top loaded.
Check out the all the Hipshot bass bridges.
This is normal.
Keep in mind -> The bass player has to be grounded. That is the purpose of the bridge ground. The bridge ground is a wire that goes from the metal bridge on a bass into the electronics cavity to the wiring harness ground.
We can create a bass that has no bridge ground if we use active EMG pickups, but all other pickups brands (passive pickups which make up nearly all, >95%, of replacement bass pickups) require the bridge ground and the players body needs to be grounded for it to work.
Our Metal Beveled fit the Trickfish IPA Bass Preamps. Both the single knob as well as the stacked knobs work on the potentiometers used with the Trickfish IPA.
Yes they fit well - Check out the Black Aluminum, Sadowsky style bass knobs.
Use the 250K Blend M/N (Aguilar Style).
T stands for Treble, B stands for Bass.
They do not have to be put as Bartolini originally assigns (T for Bridge, and B for Neck). Bartolini has wound the T pickup to have slightly more output to compensate for less string movement in the Bridge position.
Each pickup is also compensated slightly for its position, so the T is a little less trebly, and the B is a little less bass-y. You can swap them to have a more pronounced difference between the two positions.
The Sterling Stingray 5 String typically takes the OLP shape. This is the long shape WITH screw ears. The spacing matters here. If there is a big chunk of space on the ends, then it is likely 15.5mm spacing.
Check the dimensions on your bass to be sure.
This diagram (from Nordstrand Audio) shows the dimensions for this pickup
9.5” - This suits most Fender J’s except for the vintage and Flea models.
The Sire V7 basses take a size that is commonly known as the Fender American Standard 5 String size.
The pickups are roughly:
Bridge Pickup ~4.12” (~104.6mm)
Neck Pickup ~4.00” (101.5mm)
As always, check your bass. Manufacturers change dimensions on occasion.
String spacing measured at the pickup location location on the body is:
Bridge is 18mm (if measuring from the B to E = 72mm)
Neck is 17mm (if measuring from the B to E = 68mm)
*Note, this is not string spacing measured at the bridge, it is the string spacing measured at the pickup.
Both the stock pickups and Bartolini's MM pickups use a black/green/red/white 4 conductor cable.
Just swap the red for the black wires to wire a Bartolini pickup into the Sterling Stingray system.
The SMB-4A (70s style) is warmer, with less mid range, more scooped…has decent top end presence.
The SMB-4D (90s style) has more mids, less low end warmth resulting in a punchier tone.
They are two fairly distinct pickups where Duncan is trying to capture the changes in MM pickups between the 70s and the 90s.
The Warwick RockBass Corvette 5 string uses two Jazz Bass pickups that are typically thought of as 4 string bridge length. In the shop, we call them a Long/Long.
Both pickups are roughly 3.73" (94mm) in length.
On our website, this link shows the Jazz Bass® pickups available in a Long/Long configuration:
The Lakland 55-60 J bass takes a pickup size that is the same as Fender's American Standard® size.
Fender American Standard: ~4.1" (104mm) X 3.9" (99mm)
We stock more than a dozen different pickups that fit this shape.
Check them out: 5 String Jazz Bass® pickups that fir the Fender American Standard Shape
The Ibanez Mikro Basses use normal precision pickup, but and standard jazz bridge position pickup.
Any stock PJ set will match this configuration.
Click here for our PJ pickups for 4 String Bass
Unfortunately, Ernie Ball has chosen to go with a new MM pickup shape on recent models. This shape has no replacements as of the writing of this FAQ (Summer '24).
The pickup looks similar in that it has 2 screw ears on the bass side and a single screw ear on the treble side, however, the overall pickup length is not the same as the two existing shapes that have the 2 by 1 screw pattern. Bartolini will likely be introducing a pickup for this shape in the coming years.
On Warwick's Thumb 5 String basses, two Jazz Bass pickups of equal length have been used on models that we have come across. That is, the length of each pickup is roughly 3.73" or 94mm.
This 5 string size is the same size that is commonly thought of as a 4 string jazz bridge pickup length.
Click here to check out pickup sets that are compatible
*Measure and physically check your bass to see if it is compatible.
Unfortunately, the Aguilar Super Splits were dropped from the Aguilar pickup line up in the early 2020s. Nordstrand's Big Splits is what we recommend in leue of the Super Splits.
Nordstrand Big Splits 4 String
Nordstrand Big Splits 5 String
Yes - These were discontinued in the early 2020's. An excellent alternative and the likely inspiration for these pickups is the Nordstrand Big Singles. These pickups offer excellent tone and quite a solid following going back well over a decade.
Nordstrand Big Single 4 String
Nordstrand Big Single 5 String
Yes, these pickups were retired from the Aguilar catalog some years ago. There are many other good options available:
For Fender American Standard size (4.1" Bridge / 3.9" Neck) - 5 String Jazz Bass AS
For Long / Long sizes (3.7" Bridge and Neck) - 5 String Jazz Bass L/L
Indeed, the Aguilar 5P-60 pickups were discontinued in the early 2020s. There are many great 5 string P pickups.
Check our our 5 String P Bass selection here.
Yep, the 5 P/J HC pickups are no longer in production.
Check our our 5 String P/J Bass Pickup selection here.
Some basses with tight radiuses (older, vintage Fender®) are well served by having pickups that have raised centers to help the output of the center strings.
Lollar is the only one that builds their standard 5 string j pickups with raised centers. In case you are wondering why the others do not - It is likely because there are more upgrades happening on more modern basses or basses with flatter radiuses.
Lollar 5 String Jazz Bass® - Radiused
Fralin 5 String Jazz Bass®- Flat
Kloppman 5 String Jazz Bass® - Flat in both 60s and 70s
Nordstrand NJ5F 5 String Jazz Bass® - Flat both 60 and 70s
Aguilar 5J 60 5 String Jazz Bass® - Flat
Aguilar 5J 70 5 String Jazz Bass® - Flat
If you desire radiused poles from a manufacturer besides Lollar, drop us a line, and we can do a custom order for you.
Aguilar's DCB soapbars are internally wired in Series. They do not have the ability to be wired externally in series or parallel. If you are in search of a set of soapbars that can be wired in series and parallel, check out this group:
4 Conductor 4 String Bass Pickups | 4 Conductor 5 String Bass Pickups
Aguilar's MusicMan® bass pickups are wired internally in Parallel. Parallel Wiring is the traditional wiring for MusicMan® style pickups. These MM pickups are not splittable. Check out M4 and M5 at the following links:
There is a bit of an inherent challenge with getting bright and loud. To get a louder pickup, the pickup builders overwind the pickups…simply means that they wind more copper around the bobbins. Adding those extra winds increases output, but sonically, it is at the expense of top end detail/definition.
What most ears will hear from an overwound pickup, versus a standard pickup, is the that the top end (brightness) is a little lost, and the mids are stronger - kind of overshadowing the top end, and creating a somewhat darker pickup.
Generally, we encourage players to focus on the tone qualities, rather than the output levels…and adjust the amp accordingly…and also, make sure the pickups are not too far from the strings.
All that being said - I’d recommend the Delano JMVC4 FE/M2 - They have good output, and articulation. Take a look at the reviews on the following page, as well as the video demo at the bottom of the page:
https://fatbasstone.com/products/delano-jmvc4-fe-m2-4-string-hum-cancelling-jazz-bass-pickups
Several brands of bass pickups make a shape that fits the 5 string Lakland 55-02. Each of the brands from this page will have that shape on their product page.
5 string MusicMan style bass pickups that fit the Lakland 55-02
Yes, it can be wired the same way.
Yes, P2 sized pickups are often used as a replacement for the MK5 pickups, as size is almost the same, and there is a much wider selection of P2 size pickups for 5 string.
Check out our 5 String Soapbars in the P2 Shape.
There is a slight 3-4 dB lift in the lows (fundamental range) and highs (presence/sizzle range). Most players really enjoy this small contouring in their tone.
Background: The larger size has been somewhat standardized (Aguilar, Nordstrand…) for quite awhile. It is actually the hole size that has been in jazz bass plates going back many years. The hole sizes in basses are not consistent and in a couple sizes, as the bass manufacturers buy whatever inexpensive pots that they can get cheap unfortunately. Many imports use the small ones, but US manufacturers usually use the larger size.
At any rate, it is fairly common to need to enlarge the holes to get pots to retrofit.
These two couple videos use two different techniques that show how to enlarge potentiometer holes:
https://youtu.be/I3AhFfragdY?t=41
https://youtu.be/bKNAkTWC4xA
The only preamp we sell that has the smaller 7mm potentiometer shaft is from Delano.
Nope, the Fender N3 Bass Pickups are a passive pickup, and there should be no compatibility issues.
There are 3 bass preamps that are very well suited Jazz Bass® Deluxe basses:
J Retro Deluxe - https://fatbasstone.com/products/john-east-j-retro-deluxe-bass-preamp-for-jazz-bass-deluxe?variant=40267212685475
Sadowsky - https://fatbasstone.com/products/sadowsky-onboard-bass-preamp?variant=43932940402927
All include knobs and plate…and are meant to be reasonably easy installation.
The big difference between these is all in the bands.
J Retro Deluxe is a three band with a variable mid range and passive tone - but, in passive mode you can select only bridge or bridge/neck at equal.
Volume/Blend Stack -- Treble/Bass Stack -- Mid/Frequency Stack -- Passive Tone -- Active/Passive Switch -- Pickup Switch
Sadowsky is a two band with boost only on the treble and bass, but also has a passive tone.
Master Volume - Balance -- Vintage Tone Control (Push-Pull) -- Treble/Bass Stack
Lusithand is a four band that has mid separate mid controls for lo and hi mids.
Volume - Blend - Treble/Bass Stack - Lo Mid/Hi Mid Stack - Contour Switch - Passive 3 Way Tone Switch - Active/Passive Switch
Additionally - The J Retro Deluxe has a built in contour that gives a little lift to the bass and treble. The Lusithand also has contouring, but it is something that can be turned on or off via a switch.
The bushing size refers to the largest diameter part of the potentiometer that inserts through the mounting hole. This is the part of the shaft where nuts and washers are attached.
The sizes for Bartolini's Potentiometers are as follows:
Volume PushPull - 7mm
Blend Pot - 8mm
Treb 8mm
Mid - 3/8”
Bass - 8mm
Check out 2 Band Bartolini Bass Preamps
Check out 3 Band Bartolini Bass Preamps
Yes, all John East bass preamps are sold with knobs included.
Concentric pots have a upper shaft diameter or 6mm and a lower shaft diameter of 8mm.
The single pots (non-concentric) have a shaft diameter or 6mm.
Yes, this is possible. You can even bypass the blend pot completely.
There are 3 wires at the blend potentiometer: 2 white and a black on the solderless connecter.
Yes, you can! We do this fairly regularly. The list shown on the website covers the vast majority of configurations that players commonly seek out. To help clarity in choice, the list is not all incompassing.
Just drop us a line from our contact page with the desired configuration and we will let you know the possibility and cost, and we can move from there.
The FL version of the Bartolini NTMB is a 3 band preamp that is voiced for fretless. As a pre-wired harness, it has been discontinued as a production item, but we can still purchase them as special order items.
If you are looking for a 3 band prewired preamp that is in stock and ready to ship, please check out Bartolini 3 Band Bass Preamps. For 2 Band Preamps, please check out Bartolini 2 Band Bass Preamps.
Lots of great options for you with a 5 knob + 1 switch layout:
Mike Pope Flexcore - $324
https://fatbasstone.com/products/mike-pope-flex-core-bass-preamp?variant=42128495837423
Trickfish IPA - $227.5
https://fatbasstone.com/products/trickfish-ipa-3-band-internal-bass-preamp?variant=43176917860591
Delano Sonar 3MS/E - $166
https://fatbasstone.com/products/delano-sonar-3-band-bass-preamps?variant=37666820292771
Darkglass Tone Capsule - $220
https://fatbasstone.com/products/darkglass-tone-capsule-3-band-bass-preamps?variant=42671335702767
Bartolini NTMB - $252
https://fatbasstone.com/products/bartolini-3-band-bass-preamps?variant=31745658617946
Aguilar OBP3 - $230
https://fatbasstone.com/products/aguilar-obp-3-bass-preamp-custom-kits?variant=31174394773594
All are very solid preamps. You’ll notice several fall in the $220-$250 range. The outlier, the Flexcore at $324, is a bit more, as it is a true four band preamp. The Delano is much cheaper, but to some degree it is because it is unwired. It is a great preamp, and a good value.
All except for the Delano include the pre-wired cost. Some, Aguilar, Darkglass for example are sold in both pre-wired, and not pre-wired versions. 90% of sales of our preamps are the prewired versions as it saves a lot of time on your end (or your tech’s) and we can do it quicker/faster/cheaper because we do so much wiring at the shop.
We’d advise taking a look at the various preamps, the descriptions and reviews and let us know what questions you have.
There are a few preamps that are jazz plate mounted and have a side jack….not a ton, as it requires some extra difficult engineering to make these work in the space in a JB cavity.
Sadowsky:
This is a 2 band boost only preamp
https://fatbasstone.com/products/sadowsky-onboard-bass-preamp?variant=43932940402927
John East:
This is a 3 band preamp.
https://fatbasstone.com/products/john-east-j-retro-deluxe-bass-preamp-for-jazz-bass-deluxe?variant=40267212685475
Lusithand:
This is a 4 band preamp that has a contour switch
https://fatbasstone.com/products/lusithand-800jp-jazzplate-4-band-preamp-for-jazz-bass-deluxe%C2%AE?variant=44123617034479
Predecessor to the above Lusithand unit that didn’t have a contour switch
https://fatbasstone.com/products/lusithand-800ts-jazzplate-4-band-preamp-for-jazz-bass-deluxe?variant=43861906194671\
All are excellent units that have different functionality, and hence different pricing.
Essentially what you would be looking to do is cut the standard battery clip off and connect to the existing wires from the battery compartment.
In the preamps that we pre-wire, we know that many folks need to remove our clip, but we leave it on for a few reasons:
1) it gives some extra length to the wires in case the wires coming from a separate battery cavity are short
2) We test these preamps before shipping so we leave it on for customers if they have the stored in the main cavity
3) some players/techs find it easier so solder the two wires together than soldering a wire to a potentiometer
As far as soldering goes, this is pretty easy.
Once you cut the wires from the clip:
- desolder or cut the wires from your battery box, but leave wires as long of a wire as possble.
- strip about 1/2” off of each wire
- slide a 1” piece of heat shrink (usually the small size of 1/16” works well for this) onto one of the red and one of the black wires - https://fatbasstone.com/products/heat-shrink?variant=17786105921626
- twist the reds to reds, and blacks to blacks…this creates a good mechanical connection
- set a towel or some material underneath the wires, so that you are protecting the finish of your bass/and or the other electronics from drops of solder that could happen in the next step
- lay the solder pen/iron’s hot tip on the wires, while feeding in a little bit of solder to lightly coat the red wires
- repeat the above for the black wires
- slide the heat shrink over the connection
- heat the heat shrink so that it is now secure over the connection, protecting the bare wire from other electronics
The difference is minor, as it is the same preamp.
With the regular bass preamps (without the J in the nomenclature), Bartolini wires their harness in a fairly tight diamond pattern to the controls. Spector Basses, Ibanez Basses and many, many other basses do that type of layout
On the APJ the controls are wired in a line, as you would see in a Fender Jazz Bass® Deluxe.
Visit our Bartolini 3 Band Bass Preamp page.
The frequencies are fully adjustable after installation.
For any particular band, installing a jumper (jumpers included) drops frequency to the lower of the two available frequencies for that band. Conversely removing a jumper from any particular band raises the frequency to the higher of the two freq available for that band.
It’s not a huge commitment. Jumpers can be moved at any time. We usually recommend to players to use the default frequencies for a few weeks and just become familiar with the unit overall. Then when you begin to experiment with freq choice you will have a reference point from what you are changing.
Check out the Mike Pope Flexcore Bass Preamp
The passive tone control works 100% of the time, both in active and passive modes.
Yes, the tone control works 100% of the time, active or passive mode. Yes, similar to Sadowsky VTC - vintage tone control.
The trim pot is the output gain. The default setting is so that passive and active modes are about the same volume. Adjusting it up will make active louder or much louder than passive depending on how you set it. This is helpful if you have quiet pickups, or want to match two stage basses for live performance. Check out the Flexcore Preamp.
The TCT preamp only works with 9V.
Unfortunately, no. The modules will not line up right to fit in the cavity.
Fortunately, the J Retro bass preamp and J Retro Deluxe bass preamp, made by John East, do fit into Fender Jazz Basses® and Fender Jazz Deluxe® Jazz Basses.
Yes, you would want to substitute the blend to be 25k, rather than the 250k blend that is supplied with the Sonar. Same of the volume control, swap the 250k for 25k, but you should be able to use one of the volumes controls supplied with the pickups.
Yes the J Retro Bass Preamp should fit well in a Sire Marcus Miller V8 4 string bass. The J Bass electronics plate has the same dimensions, and the electronics route should accommodate the J Retro well.
Use the battery holder/compartment that your bass.
On the J Retro Deluxe, the battery connections both positive and negative go to screw down terminals, so the included jack can be removed and the basses existing wires in your bass can go to screw terminals on the preamp.
On a J Retro the positive has a screw down terminal and negative applied directly to jack. So, the included jack's red wire can be unscrewed from the preamp, and the bass's existing red wire can be screwed into that location. The existing black wire coming from the jack can be clipped, and connected to the black wire from your battery compartment.
The grounding could be done at any component as they are all grounded, but yes the loose wire at the jack is fine.
Most of our customers find connection to that wire easier than soldering to the back of a pot as it takes less heat to solder to a wire than a potentiometer.
The Lusithand 800BMF has independent buffered inputs, one for each pickup. That means there is no place to attach a single Tonestyler that has access to both pickups simultaneously.
The Tonestyler can work, but It would require two Tonestylers, one for each pickup.
Due to the buffered inputs on the 800BMF, active/passive switching is not possible.
Often the tuners that come stock on OEM basses are of poor quality, so thankfully, several tuners companies, including Hipshot and Gotoh have made replacement tuners for various bass models. Additionally, Hipshot has Bass Xtenders to do drop tuning.
Bass manufacturers change their supply sources periodically, so it is worth your time to check sizing.
The non Xtender diagram of the standard tuning machines similar naming code can be used to check for screw alignment. For Example: a diagram for an HB1 Tuning Manchine can be used to check screw hole patterns if you are considering getting a BT1 Xtender.
Here is a list of some known retrofit sizes for various basses.
Fender Squire Vintage and Vintage Modified Squire - HB1 or HB7 Tuners, BT1 or BT7 Xtender
Fender Precision Bass®, Made In Japan - HB1 Tuners, BT1 Xtender or HB7 Tuners, BT7 Xtender (may require modification)
Fender Reissue Jazz Bass® 1962 - HB2 Tuners, BT2 Xtender
Fender Reissue Jazz Bass® 1975, Made in USA - HB2 Tuners, BT2 Xtender
Fender Geddy Lee Jazz Bass® - HB2 Tuners, BT2 Xtender
Fender Jazz Bass® , Made in Mexico - HB1 or HB7 Tuners, BT1 or BT7 Xtender
Fender Precision Elite Bass 1982 - HB4 Tuners, BT4 Xtender
Fender Highway One® models- HB7 Tuners, BT7 Xtender
Fender USA Made Basses- HB1, HB2 or HB7 Tuners, BT1, BT2 or BT7 Xtender
G&L Basses - HB1 Tuners, BT1 Xtender
Lakland Darrel Jones - Hipshot Ultralight with 3/8" String post, HE6C Xtender
Lakland USA models- Hipshot Ultralight with 3/8" String post, HE6C Xtender
Lakland Skyline models - Hipshot Ultralight with 1/2" String post, HE6C Xtender
MusicMan Stingray- HB1 Tuners, BT1 Xtender
MusicMan Sterling - HB1 Tuners, BT1 Xtender
OLP Basses - HB1 Tuners, BT1 Xtender (note that their quality controlled varied at times, and some holes were slightly off)
Schaller BM Tuner Replacement- HB1 Tuners, BT1 Xtender
Schaller BMF Tuner Replacement (CBS era Fender® basses manufactured between 1967 and 1982) - HB2 Tuners, BT2 Xtender
Warwick (most models) - GB7 Xtender
Hipshot Sizing: Hipshot HB1, Hipshot HB2, Hipshot HB3, Hipshot HB7, Hipshot HB10, Hipshot USA Ultralight 1/2", Hipshot USA Ultralight 3/8"
Unfortunately, no. Unlike certain tuners from Hipshot, the Badass Tuners are not reversable to create a 3 x 1 headstock tuner configuration.
Some Sire basses have a tuning machines that have the same mounting holes as a Grover 142 Series Tuner.
Distance between top two screws is 23.5mm (center of screw to center of screw)
Distance between lower two screws is 177mm (center of screw to center of screw)
Hipshot does not make a replacement for this. However, the HB7 is the nearest fit from Hipshot. The clover key and ferrule will match but new mounting holes will need to be drilled. This is not too difficult and involves making a clean drill hole sized for a hardwood plug (Maple is a good choice), and then redrilling for new holes to fit the HB7 tuner.
The HB7 Tuners are not a direct fit. To use these, one will need to redrill the small screw holes which secure the back plate of the tuner to the back of the headstock. It is possible to use the original ferrules (in the large hole) or replace the ferrules that come with the Hipshot tuner.
Yes! Hipshot Ultralight bass tuners are reversable. The tuning peg can be switched to the other side of the tuner, allowing a bass side tuner to become a treble side tuner and vice versa. This design is great for small builders who keep a small stock of these, but can alter the tuner orientation based on custom building needs.
This video on YouTube does a good job of walking through the process. Just don't put the parts on your couch...they have a light grease on them.
https://www.youtube.com/watch?v=SEeO2q3Lizc
Click on the link to learn more and purchase Hipshot Ultralight Bass Tuners
If your bass has 5 in-line tuners that look a bit smaller than typical vintage tuners, then it most likely has Gotoh tuners.
Probably exactly the Gotoh GB707 tuners, or their precursors with the same hole size. Just in case you are looking for a more traditional look…which is often the case…. the Hipshot 3/8” Clover Ultralight Bass Tuning Keys are a match to the main hole and the screw hole -
The Hipshot Ultralight Bass Tuners are about 24g (0.85oz) less per tuner than the the Gotoh GB707.
Hipshot now recommends the HE6C Ultralight 1/2” for Rickenbacker.
Once upon a time they made an HB5 for Rick, but we believe that is now discontinued. The HB5 was a perfect match aesthetically speaking, meaning the tuner mounted to the detuner mechanism was identical tuner to the ones Rick uses.
The problem with the HB5 was due to manufacturing inconsistencies with the distance between the E and G tuners on Rick basses over the years. About half Rick owners started reporting they didn’t have enough room between the E and G tuner to swing the lever of the detuning mechanism.
We think this is why they discontinued the HB5. The HE6C 1/2”, that is recommended now, solves that problem because it is more compact, and can be installed on any and all Ricks regardless of how the tuners are spaced.
The ‘rub’ perhaps is the HE6C 1/2” is not an aesthetic match to the existing Rick tuners, but you would only notice that from the back of the bass. To make use of a HE6C 1/2”, drilling for the single screw that secures it is required, but the drill hole is under the outline of the old tuner. So if needed re-installing the old tuner covers the extra hole that had to be drilled.
The 3/8" or 1/2" measurements refer to the shaft size on the tuner, not the bore hole size.