This tool can be used to hammer on curved surfaces like rings etc. I am not sure about the name of this tool. Cobbler’s use a somewhat similar tool which they call the cobbler’s last. Message me the correct name (email at regainartntools at gmail dot com) of this tool and if you right you will win a 10% discount coupon.
please see the images for size etc. The maximum diameter of the round section is 0.7 cm. The tool alone is 65 grams. I can make a custom wooden base according to your requirement. This will give you a stable base for inserting this into. if interested email me at regainartntools at gmail dot com.