Screw thread on PH5b sight?

[fjruple]

Hi Guys and gals,
Got my first m17 and have a PH5b sight coming for it, my question is, what is the thread type on the screw that goes through the ears and into the sight? I know this has been asked before but i cant find the post.
This old girl is a .25/303 sprinter
Many thanks
Phil
Attachment 73864

I believe it's #3-56TPI.

--fjruple