The function is obvious- it cuts a groove about 1/8" wide in a concave surface. Could be like the groove for the lid in a cask but no sign of a fence to set the distance from the rim, and 1/8" seems a bit small. Tiny cask, perhaps? The stamp seems to say something like buck and hickman20170729_125321.jpg20170729_125255.jpg20170729_125241.jpg20170729_125232.jpg