Sloppy screw, gender-bender, or metric?

[ohland]

I have a screw from a C. Sharps 1875 (US made replica).

It fits fairly closely in the 8-32, somewhat loose in the 8-36 (you can rock it up and down a little), and fairly close in the M4-.7 in each of those, it will screw all the way in to the shoulder.

It will not start in the 8-40 or the M4-.5 screw checker.

Max OD of the threads is .153 / 3.93mm

Is this Metric? Sure does not act like any US thread that I have played with.

:coffeecom

[fouronesix]

I doubt C Sharps uses any metric. Sure sounds like a #8. The #8 nominal major diameter is .164. Likely an 8x32 or 8x36. Also sounds like it has been buggered, cross threaded, over tightened, changed out with wrong screw then forced or possibly started out slightly under-size. Just call C Sharps and find out what the size should be.
http://csharpsarms.com/

[EDG]

>>>Max OD of the threads is .153<<<
Find an 8-40 and an 8-32 screw and see if you can turn them in with your fingers.

I think your .153 Screw has been cut undersize.

You can check the pitch with a pitch gauge or you can mesh the threads side by side with an 8-32 screw and an 8-40 screw. The pitches have to be nearly a perfect match to mesh.

[fouronesix]

Well if the screw is loose or has play- something is not right. Based on the OP, I have no idea if it is a used gun or it's history or if the D&T'd hole is oversize or if the hole was tapped sloppy or if the screw was wrong from the beginning or if the screw and possibly the D&T'd hole both have been buggered by owner(s) (most likely cause). C Sharps should know the correct screw size and pitch. I'd think that would determine what the next step should be.

There's about a 50-50 chance that only the screw was buggered if it was cross threaded, overtightened or is the wrong screw from sometime in the past. If the D&T'd hole is also buggered, it may require a re-do. Not the end of the world and fairly simple to fix.

[zuke]

Call/email the manufacturer and ask them.

[ohland]

After I did some snooping on the internet (thanks, Al Gore!) I found that Pedersoli does an M4x.7 for it's vernier tang sights. It belongs to a Pedersoli (nice rifle!). It is not for a C. Sharps from Montana.

[montana_charlie]

After I did some snooping on the internet (thanks, Al Gore!) I found that Pedersoli does an M4x.7 for it's vernier tang sights. It belongs to a Pedersoli (nice rifle!). It is not for a C. Sharps from Montana.
If you are talking about a screw for mounting a tang sight on a Pedersli Sharps, it will be a 10-36.
However Pedersoli also ships a pair of pure metric screws with any of their long base, better grade, sights.
Those are for mounting their sights on other Italian guns.