Heavy Duty Screw Jack (with Brass Locking Screw) Features : Centering hole dia 12 mm Designed to be used for Heavy production shop. Useful completions for large clamping heights. Spindle: Carbon Steel Trapezoidal Thread Housing: High Tensile SG Iron. Pads Code P911-8/14 and 9/26 can be used for safe locating of U- Clamps.