Pro Art T Square Aluminum 18"- 1.5a�� wide light weight blade is constructed from .090 hardened, spring tempered aluminum attached to a durable plastic head constructed of impact-resistant ABS plastic. T-square is calibrated with measurements along the blade as well as along the head. One side is in inches, the other is in centimeters. Pre-drilled hole allows T-square to be hung up when not in use. Use with Pro Art Drawing Boards, sold separately.