[Corrected] 3/32 inch machine screws?

[profchris]

[Correction - I originally wrote 3/16, when I should have written 3/32]

I have bought a banjo (and yes, I know there are recovery programmes for people like me ...)

It was made in Birmingham, probably in the 1920s, and has unusual friction tuners which suit it well, so I'd like to use those if I can. The temporary tuners I've fitted are modern, and don't quite look the part.

Each tuner is adjusted with a 5/8 inch long screw, which I'm almost certain is 3/32. I've ruled out both M2.5 and UNC 2-56 by trying them (as an aside, I am probably the UK's biggest stockist of UNC 2-56 pan head 5/8 screws, as I had to buy 100, so if anyone needs some ...)

Probably these screws are UNC 3-48, but I can only buy these with cap heads, which are just wrong for the instrument. Pan head (a domed head) is what I need, two of them. Could be cut down from longer screws of course.

Can anyone help? Dig deep into those tins of miscellaneous bits and pieces, and in return I promise not to post a video of me playing the thing

 

[NazNomad]

You say 'unusual', any chance of a pic?

 

[AndyT]

That's a very odd thread. I don't have anything 3/16 with such a fine thread.

For just two screws, would it be feasible to buy the cap heads and rework them?
Maybe in a drill press with a file, if you don't have a lathe? Or I could try to turn down the heads on a few for you if you like.

 

[Myfordman]

If the thread is 3/16 diameter which is 4.7 mm why are you considering m2.5 or small American threads for something made in uk?
You have a sample screw so make some accurate measurement of diameter and pitch in inches and start from there.

 

[bugbear]

I have several thread gauges, micrometers, and have also had good results from photogrammetry/macrophotography.

IIRC you're near me, if I can help?

BugBear

 

[profchris]

D'oh! That will teach me to work from measurements, not memories of measurements.

What I need are 3/32 screws. A fraction smaller than M2.5.

So far as my researches online help, the only candidates are:

UNC 3-48, 0.99 inch diameter, 48 threads per inch

7BA, 0.98 inch diameter, 52.9 threads per inch

As best I can count, my screws are just under 50 threads per inch, so UNC 3-48 is the best candidate.

The problem with Birmingham manufacture in the 1920s is that every size of screw on the planet was available to the banjo maker. And the company made its own non-standard parts. But the maker was the UK's biggest manufacturer of stringed instruments, so I'm guessing they bought in standard parts where they could.

And my screws need to match the look of the thing, and be adjustable at gigs, not just in the workshop. So cap head is out, requiring an Allen key. Domed head is perfect, pan head would do.

I've attached a picture - the working of the tuners is completely normal, just tighten the screw enough to stop them slipping. What is unusual is the shape of the head (with the string hole) - I've not seen this before and would like to keep it.

If I can't find the right screws I might ask a US friend to search the local hardware store, but these screws seem equally obsolete in the US!

 

[profchris]

I have several thread gauges, micrometers, and have also had good results from photogrammetry/macrophotography.

IIRC you're near me, if I can help?

BugBear

That's kind! But I'm pretty sure I know what I need, the problem is finding it :?

 

[flh801978]

I can make you what you want
are you sure you want pan head? they look like round head?
pans are flat at the top rounded on the side.... rounds are fully rounded
Can you not get 2.5mm screws and run a tap down to open out to m2.5?
so to tune you get out your screwdriver loosen the screw,tune , retighten?

Ian

 

[bugbear]

Bolts with rounded threads tend to measure undersize, diametrically speaking, so I humbly suggest that

#6 BA, .1102" x 48 TPI
#4 UNF, .1120" x 48 TPI

are also candidates. (Lord, I'd hate to sort a box full of those two)

BugBear

 

[iNewbie]

Have you contacted any repairers for spares?

http://www.johnalveyturner.co.uk/page29.html

http://www.andybanjo.com/repairs.htm

 

[AndyT]

I've had another look and can come up with the following:

One only, round head, slotted, brass, 3/32" diameter 40 tpi screw, 9/16" long. According to one chart I checked, this could be an old Whitworth size. The detail of the thread form escapes me at this scale. It's probably what you want, except that it's a sixteenth short and brass coloured.

Two cheese head, slotted, plated screws which I believe to be 6BA size, so very close to the brass one in threads and diameter but again only 9/16" long.
One only, as above, but the full 5/8" long.

The brass screw is definitely 40 tpi and fits snugly into my thread gauge.
The other screws are not quite the same and don't line up perfectly with the gauge, which could be because the 6BA size is not exactly 48tpi or just because the thread form is different. However, all four screws fit easily into an ordinary 6BA nut, so unless you need the threads to mesh over the entire length, they should be ok.

If these are any use to you, pm me your address and I'll pop them in an envelope. I've probably had them nearly 50 years, waiting to come in useful, so it would be nice if someone needs them, but I won't be offended if they're not - I know they are not exactly what you want as they won't match the others, and I don't have four of anything close.

 

[CHJ]

Frustrating isn't it, boxes of accumulated screws and when you want something specific there's never one there.
6BA, 8BA odd ball metric stuff aluminium, brass, stainless aircraft instrument panel screws etc.
Only ones I have that are 3/32" diameter are steel pan head but only 7/16" long.

 

[profchris]

Thanks AndyT and CHJ for looking. Unfortunately anything shorter than 5/8 won't work.

What I think I'll do is buy 5 cap screws (£2.50 delivered) and cut slots in them for a screwdriver blade. These are black, so will disappear against the tuner button. If they fit at least I know the size I want.

Andy Banjo supplied my vellum, strings and a couple of hooks, so I'll ask next time I place an order. Or I might stumble on a hardware shop staffed by men in brown coats, in which case they'll surely have a box of 1,000 at 5p each!

 

[AndyT]

If I'm right, 6BA screws are pretty well interchangeable with the size you want. Indeed, there's a chance they are right.
There are several eBay sellers with small quantities of BA screws in whatever head you want.

 

[MikeK]

When I need obscure hardware that the local hardware stores don't stock, I go to McMaster-Carr. So far, everything I needed was a few mouse clicks away and a short wait for the package to arrive.

This link will get you close, then click on "Slotted Round Head Screws". From there, click on "Brass Slotted Round Head Screws".

 

[profchris]

The 6BA tip is v helpful - I thought these were not easily obtainable. Plenty of eBay options.

The shafts of my pegs are fully threaded, and I see that BA and UNC have different pitches. I have ordered some UNC, and if they don't fit I'll try 6BA.

McMaster Carr could help if I wanted a few thousand, but I only need 4! Shipping from the US would make these 4 screws around half what I paid for the complete instrument :shock:

Last resort will be to try to tap out to M2.5, but that risks destroying them so I'm not keen.

 

[MikeK]

McMaster Carr could help if I wanted a few thousand, but I only need 4! Shipping from the US would make these 4 screws around half what I paid for the complete instrument :shock:

I take it you didn't look at the link. The boxed quantities are 50 and 100, depending on the size, for about $7. About two years ago, I needed two 6-32 black oxide button head screws for a secure lock. The manufacturer wanted $15 each for the screws, plus shipping, but the McMaster-Carr order was less than $10 shipped. I still have 98 of the screws, but a lot more money in my wallet.

I was going to offer to help on my upcoming order if you found something that would work, but I hope you find what you need locally.

 

[profchris]

Should have been clearer MikeK - I did look at the link (100 for $7) but guessed at $20 shipping, good to hear it's only $10. Even so, that's a bit wasteful to discover that I don't need 3-48 but rather 6BA. So I've invested around £1.50 to try out 3-48 screws (with sub-optimal head) from a local supplier (added a few other bits I need to justify the minimum postage charge). If they don't work, eBay will supply me 6BA screws.

This is to be a working instrument, not a collector's restoration, so I'll live with close enough.

 

[bugbear]

Do you believe the tuners are imported American parts, in which case UNC or UNF parts are the most plausible (so #3x48 UNC or #4x48 UNF) or do you believe the tuners are British made, in which case 6BA looks more likely.

6BA and #4x48 UNF are very nearly identical :-(

6BA - 0.1102 diameter, 47.92 TPI
#4x48 UNF - 0.1120 diameter, 48 TPI

I suspect they are interchangeable, unless you're looking for a very accurate fit indeed.

BugBear

 

[Myfordman]

Do you believe the tuners are imported American parts, in which case UNC or UNF parts are the most plausible (so #3x48 UNC or #4x48 UNF) or do you believe the tuners are British made, in which case 6BA looks more likely.

6BA and #4x48 UNF are very nearly identical :-(

6BA - 0.1102 diameter, 47.92 TPI
#4x48 UNF - 0.1120 diameter, 48 TPI

I suspect they are interchangeable, unless you're looking for a very accurate fit indeed.

BugBear

It depends on how well the female thread has been cut
BA threads have an angle of 47.5 degrees and unified threads are 60 degrees so that makes the core diameter of BA smaller than the unified thread.