Serrations or other indentations on a metal surface such as a clock hand-set button, designed to improve the grip of the fingers upon it. Knurling is produced by a knurling tool which carries a hardened steel wheel with the desired pattern upon it. This wheel turns on a hardened shaft lying across a slot cut in the holder. The part to be knurled is rotated in the lathe while the tool is pressed hard against it. In mass production, special machine-knurling tools are used.