Webley Mark 3 dioptre PH16M fixing bolts?

[AC99]

I have a couple of ribbed-stocked mk3's fitted with PH16M aperture sights and the fitting bolts appear to be 4BA. I cannot find my 4BA die (mislaid!) to confirm this but I have a box of assorted BA nuts and bolts and the sight fitting bolt fits one of the BA nut exactly, so I am pretty certain the bolts are 4BA.
Aubrey

[Troubledshooter]

I have a couple of ribbed-stocked mk3's fitted with PH16M aperture sights and the fitting bolts appear to be 4BA. I cannot find my 4BA die (mislaid!) to confirm this but I have a box of assorted BA nuts and bolts and the sight fitting bolt fits one of the BA nut exactly, so I am pretty certain the bolts are 4BA.
Aubrey

I have now found out the fixing screws are 4BA as stated, but I don't know the important bit, which is the length, so if you have one to hand, the exact length would be useful to the OP.

[Mr Pusk]

Many thanks for the info. It looks like CS 4BA then, and if anyone could work out the bolt length please my joy would be complete!

[AC99]

Many thanks for the info. It looks like CS 4BA then, and if anyone could work out the bolt length please my joy would be complete!

The threaded length (up to the shoulder) is 12 mm.

[Mr Pusk]

The threaded length (up to the shoulder) is 12 mm.

Ah ha! Which sounds like half an inch in old money, or close enough. Very many thanks.

[AC99]

I forgot to mention, but I am sure you know, that a serrated (shake-proof) washer fits under each bolt head.

[Mr Pusk]

I forgot to mention, but I am sure you know, that a serrated (shake-proof) washer fits under each bolt head.

I didn't know, thanks. Just an ordinary shake-proof washer? How does it cope with the countersink, or does it just bend itself into a roughly conical shape?

EDIT: and is the serrated bit on the inside, or the outside, of the washer?

[AC99]

The serrations are on the inside of the washer and the bolt is not countersunk it is cheese-head ie square shoulders and slotted for a bladed screwdriver.
Aubrey