This Japanese manufactured early variation recoil lug (stock bolt) with the smaller size nut is for the earlier Type 99 Arisaka bolt action rifle in 7.7 caliber and is in very good condition exhibiting a brownish gray patina with some rust and light wear.  (file photo)

Note: Japanese Type 99 Arisaka bolt action rifles with the following arsenals and / or serial numbers have been observed with this part:

Nagoya Arsenal: 40856

Toriimatsu: 81817 & 99732