Cap-iron screw for old wooden plane irons - what thread?

[baldpate]

Hi,

can anybody tell me what the thread is on those big, chunky cap-iron screws used on the irons for old woodies - the sort where the cap-iron usually has a big brass nut brazed into it to receive the screw. (I don't mean the ones on Stanley/Record type planes, or the special size on the Norris adjustable).

The few I've got seem to be interchangeable, so I'm assuming that one thread size predominates. I don't have the equipment to measure it accurately, but it looks like 16tpi; the nearest BSW is 3/8", but the thread profile look too chunky to be Whitworth.

Anybody know for sure?

Thanks

Chris

 

[rxh]

It's 3/8" BSW. Here is a pic of a replacement I made for a worn screw.

 

[baldpate]

Ahh - so it is Whitworth - many thanks for that, rxh.