Martini Parker Hale PH7A Aperture issue

[Bill]

Hey fella's trying to work out if there is a thread size issue or maybe just a burr inside the PH7A.

I bought both items separately, the 6 hole Parker Hale aperture came from the UK recently and I thought it would be a straight screw in, Its seems to want to then seems to not want to, obviously I dont want to stuff threads up and research indicates both should be 7/32-40 ?? is this correct

[No1Mk3]

G'day Bill,
It may well be a burr on one of the threads, problem is it may not be 7/32x40ME, that all P-H are is a popular misconception as this is the closest commercial thread (if you can call Model Engineer a commercial thread!). The 7/32x40ME has an OD of 0.219 but Parker Hale also used an "in house" thread of 0.225 OD. I have diopters in both of these,my 6 hole P-H59 is .225" but the 3 hole is .218". I would have thought the 7A was .225" though, unfortunately I'm laid up and can't get to mine to check, Cheers.

[Bill]

thanks No1Mk3, im going with aperture having a slightly flattening of the start of the thread, Im gunna try and find a tap n die set tmw

[Bill]

got the old man to pull out a few tap n dies last nite, found a 4mm 40 tpi and gave both the aperture and sight a light clean up and the 6 circle PH aperture now screws in with the lightest of pressure, happy days...... now just need my 44 cal barrel to show up.....