The heads and tails of rivets are of various forms, several of which are shown in Fig. 334. (a) shows a cup or snap-head and tail, the dotted lines also showing a nobbled head; (6) and (c) have pan or cheese tails, and (d) has a combined countersunk and pan tail, with a nobbled head; (b) and (e) show countersunk heads.

The required length of rivet to form any given shape of head can be calculated; but in practice, on account of the clearance varying and also the cup of the snaps not always being of the same size, it is the best plan to obtain the correct length by trial.