All parts made of hardened tool steel and ground to highest accuracy. Squareness and parallelism are within .0002" per 5". Many 1/4"-20 holes to facilitate clamping. Two end rails included. .200" step built into gage block roll so that gage blocks over .200" can be used to set very small angles. 5" distance between center rolls is accurate within .0002". Offset hinge for added stability.