The 4 hole Picatinny Rail Clamp is CNC made from 6061 alum. and has a Class II Black Anodized finish. 10/32 bolts are included. Proper torque is 18 inch pounds ( use the shorter end of the Allen wrench to tighten). The side with the threads is thicker to add strength and a ‘form’ tap is used to maximize thread surfaces and strength.‍ ‍Made in the USA!