Are you sure its not just a 7/32×40 thread that has extruded slightly as it was cut, you can often find if the die is a bit dull that it pushes the metal into the shape rather than cuts.

I am assuming this sight was not original equipment on the rifle, but was fitted for target shooting. The only thing I can remember about relatively early Parker Hale sights was that the thread provided adjustment in quarter-minute clicks – in other words roughly a quarter of an inch at 100 yards. From there on, the mathematics of solving triangles is beyond me – but it could give a clue as to the true pitch of the thread. Somebody please put me right if I am talking rubbish!

Buy a 40 tpi chaser and screwcut the thread ,thats how an instrument maker would do it.Or set up a 40 tpi plug tap in the tool post and use it as a chaser,

hi,

8mm watchmaker collets use a thread which is 0.275" x 40 tpi and you can buy a suitable die for that thread, I don't know if that might help you, though I suspect you might find yourself no better than you already are in that the die might not tighten enough to bring the thread down to 0.225". Might be worth a go if your other options come to naught.

RDG Tools have them in their Watchmaker Tools section under 8mm Boley lathe accessories.

Regards Tom

Ive just been into the workshop and I can put a 7/32 x 40 tap through the mount for the aperture block, it fits but is slightly loose.

Clive

Hi Ian, You could mount a die stock/holder in the four jaw to run true and machine out a few thou, just enough so that when the die is fully open it cuts the diameter thread you need. That way if you are unfortunate enough for the die to crack it will still be located in the holder. As JS said it doesn't matter if it cracks if it's a clean break it will still locate. The advantage of doing it that way is that you can have a dedicated holder set to size and have the repeatability you require. It also saves you having to set up for screwcutting every time.

Keith

To late now and I thought I had posted this.

During training I was given several die stock to open out. The number I was told I think was by 0.015". Any larger and the die might break. I would have thought that 0.010" would be enough for many dies.

I was told that after WWII they all started coming in on size. Before that there was always enough clearance so when new ones were bought they gave one of us the job of opening them out. No problem on bigger lathes as the handles can remain on.

The idea worked too. One of the early exercises was using a die to get a precisely sized thread. 5/16 bsw if I remember correctly measured with a mic. It tools several cuts and finished up with a nice shiny thread. I suspect the tallow they supplied had something to do with the finish but very light cuts would help too.

John

–

Slightly off the topic of Dies:

Intrigued by the choice of diameter for these screws; I wondered what might be special about 0.225"

0.225 = 9/40 = #74 Drill size.

Is it feasible that Parker Hale chose to use #74 Drill Rod for its mechanical properties, and close tolerance?

**LINK**

http://timesavers.com/i-9995087-drill-rod-74-0225-x-1-1-8.html

MichaelG.

Michael, your link shows 0.0225" not 0.225"