screw slot width convention?

[Chill Wills]

(I asked this on another forum as well)

This latest large snow storm gave me a chance to spend some time in the shop. Cleaning and putting away should have been the task.
Instead I got distracted and made some screws for the low wall projects I have been trying to complete. Two screws needed are the machine screws that goes through the rear tang and the forearm screws. I made a few sets.

I've often wondered how and why gun screws have the size slots they do. They don't seem to follow any pattern or convention. Some are so wide you can't find a blade thick enough to fit it correctly and then some screws are fitted with extremely thin slots. These later, if ever hard to get out can bend the thin blades required to fit them.

I chanced learning something from the "iner-tube" (Google) whom I do not like to support in any way.... and looked for some kind of chart relating the size of slot to the standard blade with. There are numerous charts but nothing relating to what I wanted. ...No Luck!

One way to learn more would be open dad's American Machinists' Handbook, 1940.

But first, I thought it would be interesting to see what firearm specific info could be found among this group.

[Mk42gunner]

I've made a few slotted screws for non-gun projects. For the I don't care what it looks like department a useable, but ugly, slot can be made with a hacksaw. For a finer looking slot, I have used the edge of a points file (remember those?).

For a nice gun, I would make them on the narrower side, but not so narrow that you need the very thin screwdriver bits to drive them. Wide slots look tacky on a fine gun, IMO.

Best advice I can give is to make them to fit your screwdriver.

Robert

[country gent]

I have the 28th edition Hand Book Purchased around 1980) never look for screw slots in it. Ive seen some I thought were on the shallow side also.

[Scrounge]

I have the 28th edition Hand Book Purchased around 1980) never look for screw slots in it. Ive seen some I thought were on the shallow side also.

Just looked at the 5th Edition pdf of Machinery's Handbook that I have on my computer, being too lazy to walk out to the car for a newer edition. Screwdriver slots in filister head screws are .020, .025, .039, .058, .071, .086, .099, .112 inches in width, for screw heads from 1/16" to 1/2" in diameter.

You can download the book in pdf form from Google Books. This link works for me: https://books.google.com/books?id=fQ...page&q&f=false It is definitely out of copyright, but they make it hard to find unless you use the Android Play Books app. My copy is copyright 1916, the one in the link is copyright 1920. Anything before 1924 should be in the public domain now.

Bill

[beshears]

Making screws I use a hacksaw with the set ground off the sides and hold screw in Brownells screw slotting fixture, works very well. It has a guide that keeps slot centered on the screw head.

[DougGuy]

Ruger has it about right. Their screws are the easiest to work with without slipping and they can take a lot of torque so whatever convention they are following is a good one.

[Dunross]

I wish Beretta would follow Ruger in that regard then. Getting their dang grip screws out of a Model 81 was a chore even with the extra-thin bits I ordered from Brownells. Getting them out of a buddy's 22 and 25 Berettas took both of us and the guns in a vise. We got them out though and didn't mar the guns. Could have even reused the screws, but he decided to order new ones.

[waksupi]

I've had to alter screwdrivers for many guns. For wide slots, grind down the leading edge of the blade, then do some hollow grinding. I either make my own screw drivers, or buy old ones to grind down. For the very narrow slots, I hollow grind the blade to fit, then case harden the tip. On screw drivers with interchangeable bits, making narrower blades is easy, a bit harder to find fat enough bits to make them fit. If screws are very tight, I use a gunsmithing hammer to tap the end of the driver to use as an impact driver.