I really know nothing about these, but recently saw this knee mortar grenade ( totally inert and all parts screw off ). It has plenty of Japanese characters stamped on but no serial numbers on parts as mentioned here. Also the painting is different what I have seen here. I have seen here only with yellow and white straps, not red. Both black and red paint look very old and original to me.
Can someone tell me what this is.
These are the matching numbers like on weapons where parts are made and tuned to fit to each other as they are not interchangeable.
Don't know why this would be there or why it would be in English numerals.