...the size and thread pitch of the little screw that holds the safety detent in. I was playing with my A3 cycling some dummy rounds and dry-firing, when I saw something fly off, hit my shoulder and disappear. The screw backed out, and allowed the little spring to fly out. Found the spring but the screw is gone. I was thinking maybe I can find a set screw that will fit and not have to spend $5+shipping on a little screw.

I have never seen a stock M1903 or M1903A3 safety with a screw.

Can you post a picture of what you are dealing with?

There is no screw in an 03/a3 safety I just looked at mine

Pictures ??

Magazine cutoff screw maybe?

Ok, I'm stupid/Ignorant. My springfield is one of someones (probably Gibbs) reactivated drill rifles, so for some reason they must have had to modify it. Its my first and only 1903 so I had nothing to compare to, just assumed they were like this. Looked at some pictures real close and where a normal 03 safety has a small hole or is solid, mine is tapped and had set screw that retained the safety detent. They got me with this...

Empty out the shopvac.  Put a nylon over the hose and clean up the place

Here, found an old thread about Gibbs A4gerys that has a picture where you can make out the screw in the safety.
http://3gn.ar15.com/archive/topic.html?b=6&f=14&t=368873

This photo?  


That's the magazine cutoff, as mentioned by Dracster in an earlier post.  Not the safety.  The safety is the lever on the rear of the bolt, and does not have a screw.  Hence the confusion among the folks responding to your thread.

Safety on ("SAFE"):


Safety off ("READY")


The magazine cutoff, which is the part to which you're referring, controls whether rounds are fed from the magazine, or whether single rounds have to be loaded and fired one at a time while preserving the rounds stored in the magazine for later use.

Magazine feeding ("ON")


Magazine not feeding ("OFF")


I don't know the pitch of the cutoff screw.  But you can get replacement cutoff screws for $2-$3.
https://www.gunpartscorp.com/Products/515360A.htm
http://northridgeinc.com/store/index.cfm/c170/i392
http://www.billricca.com/03_springfield.htm

However, the cutoff screw doesn't retain the plunger and detent.  Those are retained by the cutoff lever itself (the part marked "ON"/"OFF").  The cutoff screw is offset to the left of the spring and detent, and merely holds the spindle in place, which is the "rod" on which the cutoff lever rotates.  (In the last photo above, it's the part that looks like a screw head, sticking out of the back of the receiver to the right of the "OFF" lever.)  


So even with the cutoff screw removed, the spring and detent shouldn't have gone anywhere, unless the spindle was removed as well.  But in that case, the entire cutoff lever would be detached from the rifle.  So I'm not sure exactly what your problem is.

If you're instead saying that there are TWO screws in your cutoff lever, the normal cutoff screw in its usual hole on the left as well as some sort of set screw to retain the spring/plunger in the smaller hole on the right. then there's no telling what kind of screw they used.  That's not the normal USGI configuration, so who knows.  That smaller hole to the right of the cutoff screw was not tapped or designed to have a screw in it.  It was simply a debris hole to allow crud to exit when the cutoff detent spring was compressed, which prevented the cutoff spring/detent from becoming fouled and frozen in place.

Its the picture before that one where the bolt is removed from the gun. You can kind-of see the screw in the safety. Not the cut-off.
Here...figured it out.
http://i206.photobucket.com/albums/bb171/sherrick13/IMG_1251.jpg
I'll just have to figure out a solution.

Ah.  Now I see what you were talking about.  That's not normally present on a M1903.

Since that's not a normal USGI part, who knows what the right screw pitch will be.  Might have to just take the part down to the hardware store and figure it out through trial and error.

Or you could replace the safety with a USGI safety.

Call Gibbs up?  They are pretty nice folks, the owner sets up at shows down here with spare parts and odd balls they get in, pretty nice guy.

This. For about $5-7 you'll never have to worry about losing that screw again.

Provided a USGI part will fit that is.

Figured out its a 10-32 thread size, so I got a 2pack of set screws from home depot and my safety is back together, with loctite this time.