Does anyone know the thread size for the threaded hole in the reciever of a Springfield Armory M1A used to attach the scope mount?

The thread is a 12-32. Tough to find a tap or die for this size but it is available. I had to make my own mounting screw. Machinery Handbook does show the thread with proper pitch diameter etc. Good luck, Gene

Would add some lock tight after setting it up. Even finger nail polish is better than nothing. Lot of "shakin goin on" beside that bolt.

If you decide not to go that route, you might look into the full rail that TROY Industries makes, it is one of the best MIL-Spec dead on fits for an M1A. Plus the rail goes past the ejector and mounts thru the sight instead.This allows you to move the scope back even further, I purchased many of the side scope mounts and found that the more expensive worked better but, for the money and the versatility of the Troy rail its money better spent,plus you have more top rail length and side picatinny rails,thus giving you more excuses to go back to the gun show and buy more sh**!
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Just stripped mine yesterday and wrote the manf. hoping to get a replacement. Bet this is going to be fun. If unavailable will hit up my bud at the machine shop.

I've got an old 1st Gen mount with the big slotted thumbscrew somewhere in the parts box downstairs. My recollection is that it's in pretty good shape. You could pull the screw out of it.
It's yours for the shipping if you want it.

The screw I made needed to be oversize. For some reason known only to God, Springfield tapped the hole oversized in terms of class of fit. I didn't use loctite because I made my thread oversize and practically sheared it into the reciever. While I was at it I made a new mount from angle iron which worked beautifully but then I'm a tool and die maker and had the machinery to do it. It's really not that hard if you've got the equipment. Gene. Oh, I forgot! that's why you stripped the screw there was a minimum of thread engagement not your fault just half assed class of fit.

PigBat, sent you a PM. Wow, thanks as getting one from PM is not going well.

I even went to friggin GRAINGER to find that screw Finally got one from John at Smith Enterprises for just 20.00 thats the 20 screw !! I finally got ride of the mount and did the TROY rail, Now I am a Railian ..Believer..

Tell you what. If you've got a friend in a machine shop I will send you a print of a scope mount that I designed for the M1-A. It works for me and I would be glad to share it with you. I made it from a chunk of 3" angle plate and it hasn't shaken loose yet. I don't have a scanner so I'll need to get it printed at Office Max. Somehow your going to need to send me your address. I don't know if the Forum keeps my E-Mail address, if so that would be a good vehicle. Gene