Figure 20. Pearl-shell hand graters (tuai). a, front and side views of short grater (C.2788) with pointed grip, thick hinge part of shell not used: 1, pointed grip end; 2, cutting edge, serrated but worn through use; 3, longitudinally concave front surface of nacreous inner coating of shell; 4, convex back, outer shell surface ground to remove roughness; 5, posterior grinding of cutting edge; length of grater, 4.3 inches; width at lower end, 1.3 inches; greatest thickness, slightly more than 0.1 inch. b, front and side views of long grater: 1, grip, rounded; 2, edge, smooth; 3, marked front longitudinal concavity; 5, posterior grinding; length of grater, 5.7 inches; width at lower end 1.6 inches; width at upper end, 0.7 inch; greatest thickness, 0.2 inch. c, front and side views of long grater with part of thick hinge included: 1, thick upper end; 2, serrated edge; 3, front longitudinal convexity, not marked; 5, posterior grinding of cutting edge; 6, thick hinge included because of extra length of grater, ground down on front surface; 7, point at which hinge part is 0.7 inch wide; length of grater, 6.5 inches; width at lower end, 1.4 inches; thickness of hinge, 0.4 inch; thickness of blade, 0.2 inch.