Help needed on taking a measurment.

[deadin]

I need some help on how to accomplish measuring for a part.
Attached are a couple of pictures of my problem. The part is quite small and I need to make a screw that will fit a threaded hole. (of sorts). The hole will pass a #41 drill (.096) and the threads look to be around 48tpi.(give or take)
However a 4-48 (and a 4-40) won't thread in. A 3-48 is too small. It just falls through.
The part is a rear sight from a pistol made in the US around 1910, so it's not likely to be metric.

Any secrets or hints on how I should proceed?

 

[Deanofid]

It probably is a #4 screw size, but may be an uncommon thread pitch. I would first try to determine the actual pitch and work from that point.

You can use a piece of paraffin wax to get the thread count. Cut an appropriately sized piece and warm it in your hand for a minute or two, then press it into the threads well. If you wipe the threads with a light coat of oil first, the wax will come out with a little coaxing. Then you can use a pitch gauge to get the actual thread count.

Brownells may or PM Research may have what you need, once you know what you've got.

Dean

 

[MikeR C]

A #3 is .099. A #4 is .112. An easy way to figure major diameter on machine screws is to remember that #0 is .060, and each number size up is .013 larger.
I looked in my machinery's handbook and saw a reference to an American National thread of 7/64-48, .109-48. My Dad was a gunsmith at one time and he left some pretty weird tap sizes.
Assuming a #4 is too big and just not threaded right, you might be looking for a 7/64-48, good luck finding a die

Thx
MikeR C

 

[deadin]

I just realized that I had a good picture of the threads that I could blow up and count them. The spread in the picture is a quarter inch and there are 15 threads in that distance, so I'm going to put the follower rest on my lathe and see if I can turn and thread a #4-60. (or thereabouts.)
Wish me luck!

Dean

 

[Kermit]

If turning a thread doesn't work out perhaps you could fill/overlay the thread with one of the low melting temp casting alloys and re tap it a 3-48?

 

[Hilmar]

Kermit,
Why can't be the thread 2.5 mm (0.098 ") X 0.48 (59TPI ) ?
Because of 1910 or US?
HM

 

[deadin]

HM,
If I can find one I'll try it. If it fits, I'm sure it will be pure serendipity.
I don't think there's any chance that a US gunmaker was using metric in 1910.
But who knows?? It's worth a try.

Dean

 

[Hilmar]

Who is the gun maker? What kind of gun?
HM

 

[deadin]

Hopkins & Allen .22 Single Shot Target.