Alvin professional drafting triangles will not discolor or warp with age and handling. The machined finish and hand polished edges of these clear acrylic plastic drawing triangles meet or exceed government specifications. All models feature a double-taper cutout center for quick, easy lifting from any angle. 45 degree (131C) and 30 60 90 degree (130C) triangles available in several convenient sizes. Alvin professional clear plastic drafting triangles.