Jag, consulting an Ithaca service manual, it could be--"brass threaded (no thread info stated), a a Lyman #10 plug , a Lyman #10D screw type OR a 6-48 RayBar." I think you said it now has a brass sight so my suggestion is to unscrew it and measure the threads. My guess is it will be a 3-56 based upon a brass sight I have in front of me. Sorry I can't be more definitive.

Last edited by Walter C. Snyder; 03/08/16 07:38 PM.

Walter c. Snyder