[Corrected] 3/32 inch machine screws?

[Cheshirechappie]

They may not be UNF or UNC - Unified threads only came about after WW2, following difficulties experienced by the military matching US and UK made equipment. Prior to that, the UK tended to use BSW and BSF for larger items, and BA for instruments and smaller items; the US used American National standards, which are not quite the same as Unified in all cases.

My guess for something made in the 1920s would be a BA thread, but without showing them to a micrometer an thread gauge, it's impossible to be sure.

Just in case, here's a supplier of small screws dealing mostly with the model engineering market. They stock roundhead brass BA screws, and are happy to supply small quantities - just one screw if that's all you need!

http://emkaysupplies.co.uk/

(PS - Sorry for not mentioning this earlier - only just spotted the thread!)

 

[profchris]

Thanks again to all posters. 6BA is next on my list if the UNC ones don't fit, and that's a useful link CheshireChappie (looks like I can choose steel or brass, steel would be more in keeping I think).

With friction tuners like this it's easy to strip the internal thread by using a screw that's close but not exact (two tuners have these, one countersunk, the other hex head) so it's good to know the difference between BA and UNC. I'll keep my fingers crossed they're not National!

 

[profchris]

Hurrah! UNC fit.

Though, holding them up to the light against the original screws (both in front and behind), the UNC are just a fraction thinner. But the threads mesh, and the new screws run all the way down the tuner posts without binding or feeling loose.

Bugbear, you seem to be the BA screw guru in this thread. My 3-48 UNC fit, so 6BA is clearly too big. I guess the originals might have been 7BA, which seem to be obtainable only in sizes which are too short for me.

Even the socket cap heads look OK, in black to match the buttons, but the 2mm Allen key will go missing in seconds. Once all four tuners are fitted, the other job today is clearly to make a handle for the key.

 

[AndyT]

Yea! Once more, the collective power of the forum triumphs over the dark forces of obsolescence. =D>

 

[profchris]

So nearly, but not quite

The thread in the fourth tuner I fitted (and it always has to be the last one) has been damaged by the misfitting countersunk screw that was in it, so the UNC screw slips. Fortunately the right sized screw (I have two) still works in the thread, so the old tuners are back on and work fine.

Interim fix - cut slots in the cap head bolts to take a flat head screwdriver, so as least I can adjust them all with the same device.

Long term fix - either find two long 7BA screws (if that it in fact what I need) or go mad and tap them out to M2.5 and risk buggering them completely.

Heigh ho!

 

[bugbear]

Hurrah! UNC fit.

Though, holding them up to the light against the original screws (both in front and behind), the UNC are just a fraction thinner.

I hate to ask but; you DO own a micrometer, don't you? I mean, everyone does, so it seems likely...

BugBear

 

[profchris]

Micrometer? I make things out of wood, and if I get within 0.5mm I'm content. All those neat-looking joints on my musical instruments are made by attaching bigger bits and then planing/sanding them back to fit.

I buy in metal stuff, when I can't scrounge it from the folks on here

After lots of head shaking over tables of screw sizes I've decided that 7BA is as thin as my UNC screws, so I need to try 6BA. Their measurements seem a hair too big but maybe the rounded profile on the thread makes them just right. Anyway, 6BA screws (with nuts, so I can make use of them if the wrong size) are on order.

I'll probably find these were M2.5 all the time ...

 

[AndyT]

Look on the bright side - you're building up a stock of odd sizes of screws so you'll be ready for the next similar job when it comes along.

Have you got enough old tobacco tins?

 

[profchris]

I plan to store them the traditional way, all mixed up in the same tin together with miscellaneous metal items whose purpose I've forgotten..

 

[profchris]

Bugbear is The Man!

6BA screws arrived today and, lo, Cinders shall take her banjo to the gig. I know, I know, if only I owned a micrometer all this hoohah could have been avoided.

And the tuners work more smoothly with the right sized screws (unexpected, the slightly undersized 3-48s still nipped them up tight). I might even solve the great unanswered question, "How long does it take to tune a banjo?"

 

[novocaine]

"How long does it take to tune a banjo?"

nobody knows.

how do you tune 2 banjos? you shoot one of the players.

 

[bugbear]

Bugbear is The Man!

6BA screws arrived today and, lo, Cinders shall take her banjo to the gig. I know, I know, if only I owned a micrometer all this hoohah could have been avoided.

And the tuners work more smoothly with the right sized screws (unexpected, the slightly undersized 3-48s still nipped them up tight). I might even solve the great unanswered question, "How long does it take to tune a banjo?"

I am very happy that it all worked out.

A micrometer is pretty handy, but is not the sole requirment for identifying threads. Thread gauges are also required (because OD varies with tolerance/wear, enough to make similar threads ambiguous). I currently don't have a BA thread gauge, so I use BA taps as comparators...

Micrometers are useful in general though. (how else would you measure shavings? )

BugBear