# Coarse Spline 1/4" Knobs



## THRobinson (Jun 29, 2014)

I have an old guitar needing knobs. I tried the common 6mm coarse spline and not big enough. Cracking the plastic.

Looks like they're 6.35mm / 1/4" shafts, but not fine splines like a CTS. 

I can find 1/4" fine, or 6mm coarse... but not 1/4" coarse.

Anyone ever see these as 1/4" coarse? wouldn't have thought they'd be that uncommon....


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## greco (Jul 15, 2007)

I'm assuming that you checked Next Gen?


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## THRobinson (Jun 29, 2014)

Yes....

A - They don't sell that style
B - They don't seem to list shaft size... just 18 or 24 spline, solid or split shaft

So, I assume the 18/coarse is 6mm and 24/fine is 1/4".


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## Lincoln (Jun 2, 2008)

Knobs


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## THRobinson (Jun 29, 2014)

Lincoln said:


> Knobs


According to the Q&A they fit 1/4" fine... not 1/4" coarse.

Again, very odd that combo is so hard to find, but, they are 50yr old pots and no idea who made them. Easiest thing would be to replace them but, guitar is still all original and they work.


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## jbealsmusic (Feb 12, 2014)

THRobinson said:


> I have an old guitar needing knobs. I tried the common 6mm coarse spline and not big enough. Cracking the plastic.
> 
> Looks like they're 6.35mm / 1/4" shafts, but not fine splines like a CTS.
> 
> ...


Just to clarify for the OP, and anyone else following this thread. No one makes 1/4" (6.35mm) split shaft splined pots in our industry. They are all 6mm.

The shafts commonly used in the guitar industry are as follows:

6.35mm solid shaft
6mm solid shaft
6mm split shaft, "fine" 24-spline (CTS, Emerson, Gibson, Fender, etc.)
6mm split shaft, "coarse" 18-spline (import/metric guitars)
Splined split shaft pots are always 6mm. The only difference is whether they are 18-spline or 24-spline.



THRobinson said:


> According to the Q&A they fit 1/4" fine... not 1/4" coarse.


The Q&A info is technically incorrect. People casually refer to split shaft pots as 1/4", but that is only a colloquial/nominal term. It is not technically correct because those knobs actually measure 6mm.

Please help us spread the correction to this common misconception!


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## greco (Jul 15, 2007)

jbealsmusic said:


> Splined split shaft pots are always 6mm. The only difference is whether they are 18-spline or 24-spline.


Thanks for the clarification.

Now that 6 mm is a standard for splined split shafts, it certainly would be wonderful to also have a standardization of the number of splines.


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## THRobinson (Jun 29, 2014)

@jbealsmusic ...so, the pots I have in my hand don't exist? Whew... that's a relief!



They may not make them anymore, which is what I needed to find out, but they obviously existed at one time because well, measured them and compared them to metric pots I have, even got the jeweller's loupe out and counted the teeth on the shaft. May just have to drill them out a bit. If not for damaging the pots, I'd heat the shaft up and melt them onto it.

So... for the most part then metric/imperial refers to the threaded parts of the shaft then I guess?

Are you sure there are no 6.35mm split shafts? For example, I found this diagram for Seymour Duncan pots


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## zztomato (Nov 19, 2010)

Find the appropriate drill bit and open up the knob a bit- do it by hand. You can use black paint or nail polish to paint the interior of the knob after if needed.


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## greco (Jul 15, 2007)

zztomato said:


> Find the appropriate drill bit and open up the knob a bit- do it by hand. You can use black paint or nail polish to paint the interior of the knob after if needed.


This is exactly what out local guitar tech told me to do.


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## THRobinson (Jun 29, 2014)

THRobinson said:


> May just have to drill them out a bit. If not for damaging the pots, I'd heat the shaft up and melt them onto it.


Yup... already thinking I'm stuck doing that... though not by hand. I'll likely glue them down stable on some wood and drill press them slowly. Probably hot glue... give it a second to cool a bit but still liquid and tack it down. Stuff peels off easily enough. Just need to tape up the top else pull off the lettering.

Reminds me of when I had a Peavey Bandit 112 silver stripe amp, and they used a very odd shaft size for that 1 model only. 4.7mm I think it was.... my old post for it keeps getting resurrected because people still can't find knobs to fit. In that case I was lucky. Shaft was smaller than the knobs, so used heat shrink tubing on the shaft. 2 layers and the knobs stayed on. Now I have the opposite issue.


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## jbealsmusic (Feb 12, 2014)

THRobinson said:


> @jbealsmusic ...so, the pots I have in my hand don't exist? Whew... that's a relief!


Lol. Invisible pots are the best kind of pots! 

In all seriousness, I'd bet if you measured the shafts using a calibrated micrometer, you'd end up with somewhere between 5.9mm and 6mm. Out of curiosity, what is the guitar?



> So... for the most part then metric/imperial refers to the threaded parts of the shaft then I guess?


I have taken to using actual measurements more and more, as generalizing only seems to lead to further confusion down the road. I wish this industry were so simple as to be able to put things into general categories like Metric vs Imperial or Import vs USA. Sadly, the longer I do this, the more I see it is often more complicated than that. 



> Are you sure there are no 6.35mm split shafts? For example, I found this diagram for Seymour Duncan pots


Can you share where you found that diagram? If it came directly from Seymour Duncan, they should probably be notified it is wrong. I know with 100% certainty that our push-on knobs fit on Seymour Duncan split shaft pots. If their pots were actually 6.35mm, they wouldn't fit. In fact, it would mean that none of the push-on splined knobs on the market today would fit on their pots.


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## Silvertone (Oct 13, 2018)

This drawing does not seem to be to scale, so very likely someone said, hey they must be 1/4" then did the conversion and labelled that way. I am a CAD monkey by training and that kind of stuff bugs me. I doubt the splined shaft is wider in diameter than it is long.










Cheers Peter.


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## THRobinson (Jun 29, 2014)

Guitar is a late 60's Vibra SG... I used a set of digital calipers to measure it and measured a new set of pots I had because I knew they were 6mm and wanted to see if the calipers were being accurate and they were. The Vibra definitely has a 6.35mm split shaft with coarse splines.

Agreed about the metric/imperial... honestly, if the USA would quit being difficult and switch over to what most of the world now uses, we'd likely not have this issue. My belief is that the Americans don't like metric, simply because they didn't invent it. 

Diagram wise, I just searched potentiometer measurement diagram and it was the first one I saw with 6.35 and knurled... I guess just right click it, and in the menu (if using Google) left click "search Google for image".

Lately, all my pots are metric CTS pots with coarse splines. Yup... they exist... great for import upgrades because knobs fit and don't need to enlarge the mounting holes. I prefer Bourns but, these are easier. Like I said, normally I'd save the headache and swap pots, but, on old guitars (cheap or not) I like to keep it all original if I can.


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## jbealsmusic (Feb 12, 2014)

THRobinson said:


> Guitar is a late 60's Vibra SG... I used a set of digital calipers to measure it and measured a new set of pots I had because I knew they were 6mm and wanted to see if the calipers were being accurate and they were. The Vibra definitely has a 6.35mm split shaft with coarse splines.


Well, colour me shocked! I would venture to say you won't find knobs that will fit. At least, not easily... You'll most likely need to modify the knobs you have.



> Diagram wise, I just searched potentiometer measurement diagram and it was the first one I saw with 6.35 and knurled... I guess just right click it, and in the menu (if using Google) left click "search Google for image".


Found it. That pic is from a Brazilian online marketplace. Not sure where they got it though, because it isn't from SD. Weird...



> Lately, all my pots are metric CTS pots with coarse splines. Yup... they exist... great for import upgrades because knobs fit and don't need to enlarge the mounting holes.


Yeah, people forget that pot companies are pot companies, not guitar parts companies. They just make whatever their customers pay them to make. There are all sorts of options for dimensions, materials, tapers, tolerance, and torque, just as a starting point. It just so happens that most people in our industry ask each brand to do the same stuff all the time, so that's what they become known for. 

CTS with smaller/metric bushings and 18-splines? Why not? Alpha with brass shafts/bushings, imperial thread, higher-life track, and 24-splines? Alright! On one hand I'm really excited at all the new options hitting the market. I love options... On the other hand, more options leads to more market confusion. So, it's a tricky line.


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## THRobinson (Jun 29, 2014)

Yup.... just make 18 splines or solid shaft... 6mm for both, and done. No advantage really in almost proprietary pots and knobs.

Like I said, that Peavey amp had 4.7mm shafts and only for the silver stripe amp.... no one can find knobs for that anywhere, except I think they make them for ovens/stoves. Instead of an amp that goes to 11, you can have one that goes to 500.  That said... internally, the pots were standard smaller sized board mount... if I were keeping the amp, I'd have swapped the pots.

... reminds me, I need to go to NextGen this week (online) and get some binding.


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## THRobinson (Jun 29, 2014)

deleted


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## jbealsmusic (Feb 12, 2014)

THRobinson said:


> deleted


Oh man... Just missed it!  Wonder what it was...


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## THRobinson (Jun 29, 2014)

@jbealsmusic haha, yeah... i was trying to find knurled inserts for knobs, for if you made your own knobs. Didn't find any and thought maybe you'd know... then literally 30sec after I posted I found some.


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