Confused on a thread size???

[srk]

Howdy
I have an 1885 low wall, original, in .32-20.
I made a tang type peep sight for it and have stumbled
on a thread size that has sent me for a loop.
Now I have been a Tool maker for 25yrs and the long
bolt at the rear of the gun measures .209-.210 dia.
If you do a quick calculation to metric it comes out
a little more than 5mm.
Is it possible it has a metric bolt, even though the front
screw is a clear 10-32?
The bolt is tapered top to bottom starting at .225 approx. down to
the .210 approx dimension.
Can anyone shed some light on this for me?
Thanks
Srk

[country gent]

Winchester may have used a tapered screw body tapered as you measured to thread/ What is the major threads dia. Or the threaded hole size? Could it be a 12 X32 thread? At the age of an original it is more than likely an american thread pitch but dia could be a off size for manufacturing purposes

[srk]

Hi
I was thinking the same.
If you do the conversion 12x13+60=216
Which is approx same major diameter as the screw at the thread end.
This is the formula for calculating major diameters on number type threads ie 10-32, 10x13+60=190
So I figured the threads per inch at 32 as well.
But never heard of a 12-32 thread.
Im either going to have to make one, which involves making a tap and die,
or I will have to modify my lower mount.
Life is never easy.
Going to try and find one
Thanks
Sean

[country gent]

I would also check for 48 tpi as that is national extra fine series/ there is a 12 screw thread it should be shown in the machinists handbook. Are the threads in the tang damaged? the screw could be turned up pretty easily and threads cut single point on the lathe and measured with thread wires or fit to mating hole. The big thng is getting dias right on the taper and its length if it is a mating hole. Scope screws sight mounts and most firearms prts use the 48 tpi serioes. Look the 12 thread up in the machinists handbook it will give all needed dimensions and form in a chart. In 35 years as a tool and die maker i did memorize decimil equivelents some other info but never the thread charts LOL.

[William Yanda]

1885 was before threads were standardized. Some tool makers-Stanley anyone-were notorious for using a proprietary thread.
At that point in time Winchester may very well have done the same.

[srk]

Going to double check o.a.l of screw against the spot face I
put on the mount.
Might be able to get away with just counter sinking the hole
without losing too much travel/length.
This will also help keep it in relative position If
IF ever have to take it off.
Hi P.B thanks for your input.

[FrankG]

srk ........Im curious........where did the '13' come into the figuring out the thread dia.?

[srk]

Hi Frank
Its part of the formula which is "x (thread designation) x 13+60= Major diameter
Now this formula only applies to number thread sizes ie: 5-40, 6-32, so on and so on.
Where it came from, I have no idea.
I found it in the back of a Starrett catalolgue back in high school.
And kept it in the old memory bank.
Hope this helps!
All the best
Sean

[John Taylor]

The originals were supposed to be .205 X 28. I had several taps made but they all seem to be on the small side. A 12-28 works fine if not a little loose. the other hole ,should be a 10-36 ( book says 10-35.5)

[FrankG]

Thanks Sean ! More good info to store away !

[Bent Ramrod]

The ones I used to make had a 0.208" x 28 TPI section 0.360" long. It then tapered at about 5-1/2 degrees for 1.150" to a diameter of 0.229". This diameter held for a 0.063" straight section, then the head of the screw was 0.268" in diameter, if a Lyman tang sight was to be fitted. The bottom of the head of the screw needed to be tapered to fit the socket in the Lyman sight and the top rounded and slotted.

The threaded section may have deliberately been made long so I could shorten it as needed to fit; can't remember any more.

When a factory was set up in the old days, the toolmakers didn't care what threads or sizes were specified, and the engineers only cared if everything fit together properly according to their ideas of reliability and longevity. Plus the company had a captive market for spare parts and none of the liability that might occur if the customer "repaired" his gun with a hardware store stove bolt.