Zinc plated steel.
Non tiltable, and I wouldn’t use one for a large aerial.
Some people buy these to use the V bolts for something else, the I.D. (inside diameter) of the V bolt is about 56mm and the length (from the shoulder of the V) is about 80mm.
Please note: The purchase of a separate clamp is not required for any of our aerials, because they’re all supplied with one !