Replacing Metric Lock Screws

[Ky-Flinter]

I'm getting some stuff together for my nephew's CVA Kentucky project.  I sure would like to replace the OE screws that hold the lock in.  They are 4mm x .70 pitch. 

Is there enough material to drill and tap the existing 4mm holes for 8x32?  I looked at some drill/tap charts on line to compare the sizes and it just made me dizzy!@#$%   

Or, is there someone that sells 4mm x .70 screws with an appropriate domed and slotted head?

Any ideas?   Thanks.

-Ron

[Curt Larsen]

I guess if it were me that I would just get replacement screws from CVA rather than messing up the lock by cutting new threads.  I also seem to have read somewhere that U.S. military used metric threads for a long time before switching to English threads.  Maybe there are some that would fit if you looked hard enough, but I would just try to get new lock bolts from CVA.

[Dphariss]

I guess if it were me that I would just get replacement screws from CVA rather than messing up the lock by cutting new threads.  I also seem to have read somewhere that U.S. military used metric threads for a long time before switching to English threads.  Maybe there are some that would fit if you looked hard enough, but I would just try to get new lock bolts from CVA.

There is a metric thread, I am told, that is very close to 10x28 and this causes some confusion.
19th century firearms often had odd thread pitches and people will confuse these with metric.
Winchester used 10-36 and 11(?) 32. Most of the screws on a 74 Sharps are 10x28. 10x28  is a "NS" thread "National Standard" as is the 10x36.
The "normal" fine and coarse thread pitches are UNF and UNC. But these were not finalized until well into the 20th century and even then there are special pitches found in firearms that are neither to this day.

While its possible that some military firearms may have used metric threads, we did copy French Muskets after all, it was not an ongoing thing so far as I know.

Dan

[D. Taylor Sapergia]

When I encounter this sort of thing, I find a screw that measures a little bigger than the one in hand, and go ahead and drill and tap for the 8 or 10 screw.  I wouldn't hesitate.

[Ky-Flinter]

Thanks guys.  My apologies, my original post wasn't very clear on the actual issue.  I should have said I don't have a problem with the metric threads.  It's the butt ugly, flat head, countersunk, too small head on the CVA screws.  I want a proper looking flat bottomed, domed head and could care less about the threads, as long as they work.  So, I'm looking for replacement options for all the screws on this gun.

There is a metric thread, I am told, that is very close to 10x28....

The OE tang screw on the CVA is a 5mm x .80 pitch.  A 10x32 is almost identical, so that problem is solved.  I have those on hand.

Thanks Taylor.  I have some proper 8x32 lock bolts on hand, but I'm not sure there is enough material left in the existing 4mm hole to drill and tap to 8x32.  Was hoping someone had done this before.

Will have to ponder on this some more before proceeding.  Thanks for the help.

-Ron

[D. Taylor Sapergia]

I'm sure I've replaced European crews with American for just the reasons you have said, but I honestly cannot give you a positive answer with particulars.  Sometimes you have to go out on the end of the plank all by yourself, and see what it's like.  If it doesn't work with 8 x 32 you can always go to 10 x 32.  Since I bought my lathe, I just make the screws I need.  Before the lathe, I used my drill press and a file.  Before the drill press, I squeezed my electric hand drill in the vice, and used a file.

[Clark Badgett]

I looked it up once when I was playing around with a WW2 Russian Mosin (all made with English threads), and found that AK accessories (made with metric threads) fit the cleaning rod. My Machinery's Handbook is at work but I think it was the 8-36 that was for all intents and purposes the same as the M4x.7. So if my memory is correct drilling and tapping for a 8-32 won't work, but you can take it to 10-32.

[Ky-Flinter]

Update.  I was able to get some 4mm x.70 nuts today.  Drilled one with a #29 drill and ran the 8x32 tap thru it.  Worked fine, so I went ahead and tapped the CVA lock plate.  Also working fine.  Thanks for the inputs.

-Ron

[Clark Badgett]

Maybe it was the M5 that was the same as the 8-36.

[Wyoming Mike]

I have replaced CVA lock screws with 8x32s many times.  I just ran an 8x32 tap into the existing hole and it worked out fine.  These screws don't have a lot of pressure on them so just running the tap through the existing threads won't cause any stripped holes or screws.

BTW: The metric tang screw on a CVA is an exact match for a 10x32.