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I purchased a set of Parker screws from Galazan. The first set had threads that were only cut to about half depth. A very nice lady at Galazans worked very hard over a period of a month trying to send me good ones. When they arrived they were very nicely cut and formed to the mazimum size. They DO NOT fit any vintage Parker but may be perfect for repro's. It turns out thread sizes were not standardized until WW II. If I can find a 10-36 die I hope to save then by adjusting the die size to minimum. Hunt a friend with a lath and forget this scource.
bill

How do the heads look for a vintage Parker? I've been thinking about ordering a set, and if the heads are "right" it might be easier to recut the threads than to have new screws made. Chuck H opinion?

I don't know about the Galazan screw set but a while back I needed a screw for a DHE Parker forend and I had to have one made up in a machine shop. I remember the shank was a #10 but I don't remember the pitch. Maybe it was 36 tpi??? The thread diameter was undersize as compared with the current industry standard. Sounds like this is similar to your problem. The split die would work and I'm sure you can find one at Brownells and/or McMaster. It's going to be tough to grip the screw to cut the thread undersize, without damaging the screw slot or the shank. I've done that myself by squeezing it in a vice between two pieces of soft aluminum flat stock. Hope this helps. Silvers

Without measuring it, I can't give you advice on the way to go. It's certainly a pre SAE, ANSI, or MIL-105 thread size. I'm guessing it was a 3/16"-36 (if it is 36 tpi). Pitch dia might have been something that was sorta standardized among certain industries or within a country or region. Maybe even a British thread.

If you have a friend with a machine shop, he may have an optical comparator. This is basically a projected light with a focused, magnified shadow image displayed on a frosted screen. The screen has measuring increments and angle measuring capability. This will identify the thread flank angles and pitch redily and can even measure pitch diameter if it's a good one.

Failing the availability of an optical comparator, a set of pitch gauges and some pitch wires and a micrometer and you'll be able to learn enough.

If you find the pitch to be 36 tpi and the pitch diameter to be slightly under a #10-36, Rutland Tool has a 10-36 split button die for $12. http://www.shoprutlandtool.com/webapp/wc...1=&scFlag=0

Be darn sure it's a 36 before you run the die on it or it'll make a mess. And remember, a button die has a cutting lead that won't cut full threads to the shoulder of the screw unless you flip it over and use the 'backside'.

To hold onto a screwhead that has a straight o.d. like most action screws, drill/ream a nice hole the same diameter as the head of the screw in a small block of aluminum or brass and split the block on one side with a saw. Put the block in a vise and tighten with the screw in place and the threads protruding upward.

And I thought I had a lot of respect for Çhuck before! Wow! I'm impressed.

In going along with what Chuck said, along with buying a split die, one that you can adjust the depth of the cut, I would also buy a chasing die. These aren't split and are hex shaped so that you can use a wrench on them. They also have to be turned around to get close to the head. You have to make sure before using this die that the threads are full depth in the piece you are fitting it to.
The trouble with recutting small screws close up to the head is that the holder of the die is usually in the way of getting close to the head. One way to do it would be to use the holder to start the thread, then take the holder off and use a pair of pump pleirs on the die and chase it to the head. The die is hard enough that the pliers won't hurt the die. Just don't put a lot of pressure on the die with the pliers.
You would need an adjustable die, to keep trying the fit to get the right depth in the thread
Another way would be to buy an acorn die and holder. The holder is adjustable in the deph of cut, not the die. In my opinion the acorn die is easier to use.

The head diameter was perfect and the head is THICK. It was so thick that I am able to tighten a screw into place with the existing slot, mark the indexed location, cut a new slot and then dress it down to the action. If you are worried about cutting the slot I used a Vermont American 32 tooth/inch copeing saw blade. The thickness is perfect and the blade is about .250 tall and stiff. Does a perfect job, of the correct width, for a small investment. I use watch makers files for tiny screws but the copeing saw is great for a lot of mid sized screw slots.
bill

I have an old Brownells Parts and Assembly book that has all the screw sizes for a Parker. According to this reference the trigger plate screws are supposed to be 8/36, I measured an old screw and the thread was .168 OD. If the screws that Bill had were 10/36 it would explain the reason they would not fit. This screw should be easy to make on a lathe.

"that screw should be easy to make on a lathe"
Unless you had access to a screw machine, that size would be imposssible to make on a lathe.

Unless you had access to a screw machine, that size would be imposssible to make on a lathe.

Maybe on a harbor freight toy, I have a 1947 South bend Lathe that I make screws on all the time, you just need threading capability.