HHIP Precision parallel set includes 1/2" x 7/8" x 6", 1/2" x 1" x 6", 1/2" x 1 1/8" x 6", 1/2" x 1-1/4" x 6", 1/2" x 1-3/8" x 6", 1/2" x 1-1/2" x 6", 1/2" x 1-5/8" x 6", 1/2" x 1-3/4" x 6" size. Made from fine qualify tool steel stress relieved against distortion, precision ground and hardened. These precision parallels are recommended for layout work, standards and set up. The holes are designed for easier handling and set ups. Hardness: case hardened RC 55 to 62 on 2 sides, top and bottom only. Complete with fitted durable plastic case. Tolerance: Parallel To 0.0003 on 2 sides, top and bottom. Dimensions: within 0.001" allowance.