Bell screws?

[tubajeff]

I have two project horns with removable bells (a Martin euph, and a Holton 6/4 109 short action tuba). The thread size for the missing bell screws seems to be #12-24 for both. But that seems to be the one size that hardware places don’t stock for brass thumb screws with the knurled caps. They skip from #10 to 1/4-20. Anybody have any leads, or am I missing something? I found exactly one listing on eBay asking $145 for 100 of them, which seems overkill since I only need about 5. Thanks for any ideas...

[bloke]

I wonder what would happen if you talked to Curtis Ferree really nicely, and asked him if you could pay him to turn some of his 5/16 X 24 bell screws down to 12 X 24 (which is basically 7/32 X 24)...??

https://www.ferreestoolsinc.com/product ... ell-screws

[tubajeff]

Thanks bloke. The tuba might actually take 1/4-24 size. Then I’d only be short 1 smaller one for the euph.

[Yorkboy]

1/4-24 is an extremely unusual thread count - the only time I’ve encountered that size is when rebuilding Model T Ford magnetos:

https://www.modeltford.com/item/3278RE.aspx

1/4-28 is SAE, and much more common (not saying that yours isn’t 1/4-24, it’s just an odd size).

Anything in a 12 diameter seems a little small for a tuba bell screw (?)

Short of anything else, bloke’s idea seems like a good one.

Or, if you were handy with silver solder, and the pitch is actually 24 TPI, you could buy some of those Ford magneto screws and silver solder on a knurled top cut from another generic screw…….

[bloke]

"...thread not to know
For what the bell screws,
An Olds for thee."
- Done.

[tubajeff]

For reference, the 1/4x24 screws did fit the Holton 109 (short action) tuba.
I’m thinking of just shipping the whole Martin euph project (missing 1 of 2 #12x24 screws) to bloke to get it restored properly. The missing screw is the easiest problem to sort on that one. I think it could be a really special horn if done well and I don’t have the tools or skills. I’ll send you an email

Thanks again for the help