Scope mount rail thread size?

[LawrenceN]

I'm mounting a scope rail on my SKS and as near as my tired old eyes can make out, the thread size for the mounting screws is 6-42. The scope rail is made by Millett for the Remington 7400/7600 series rifles. Can anyone verify the thread size for me? My go-to guys here can get me the tap I need to mount the rail if I have the size and pitch correct. Thanks in advance.

 

[hunter5425]

Most screws for mounting scope bases are 6-48 or 8-40 so you need a 6-48 tap which is not common but can be ordered from Brownells ( there is also a Canadian supplier but I forget who).