Fig. 370.
The heads of bolts are designated by their shapes, irrespective of whether they are left black or finished. [Fig. 370] represents the various forms: a, square head; b, hexagon head; c, capstan head; d, cheese head; e, snap head; f, oval head, or button head; g, conical head; h, pan head; i, countersink head.
The square heads a are usually left black, though in exceptional cases they are finished. Hexagon heads are left black or finished as circumstances may require; when a bolt head is to receive a wrench and is to be finished, it is usually made hexagon. Heads c and d are almost invariably finished when used on operative parts of machines, as are also e and f. Heads g are usually left black, while h and i are finished if used on machine work, and left black when used as rivets or on rough unfinished work.
Fig. 371.
