snaphead

Century Dictionary and Cyclopedia

1. n. A riveters' swaging-tool, used in forming the rounded head of a rivet when forged into place.
2. n. A rounded head of a rivet, bolt, or pin.

Wiktionary

1. n. A hemispherical or rounded head to a rivet or bolt.
2. n. A swaging tool with a cavity in its face for forming such a rounded head.

GNU Webster's 1913

1. n. A hemispherical or rounded head to a rivet or bolt; also, a swaging tool with a cavity in its face for forming such a rounded head.