This Japanese manufactured rear sight base screw is for the Type 44 Arisaka bolt action carbine in 6.5 caliber and mounts on the underide of the rear sight base holding it to the barrel. This screw is in very good condition exhibiting a brownish gray patina with some slot wear.  (file photo)

Note: Japanese Type 44 Arisaka bolt action carbines with the following arsenals and serial numbers have been observed with this part:

Koishikawa / Kokura: 019478 & 47028