Alvin drafting protractors are constructed of heavy-duty 0.090" transparent laminated PVC plastic with a beveled outer edge for accurate drawing. Each protractor features a center cut-out for convenient finger lift and accurate die-stamped graduations. Available in round, half-round plastic. Helix protractors are ideal for math students, artists, architects, more. General's protractor used for setting bevels, measuring, and transferring angles. Durable stainless steel construction. Alvin, Helix, and General professional drafting protractors.