The Multi-Clamp (formerly known as Safari Clamp) is precision machined from solid blocks of 6061-T6 aluminum. The hardware is stainless steel. The Multi-Clamp securely mounts to any round stock up to 3.5 inches (89mm). Or add the optional Flat Surface Adapters to mount to any flat surface up to 2.4 inches (63mm) in thickness. There are five threaded holes in the Multi-Clamp: four 3/8"-16 threaded holes, and one 1/4"-20 threaded hole. Use these built-in sockets to mount your attachments. Features: CNC machined 6061-T6 AluminumAnodized; Type II BlackFour threaded 3/8"-16 holesOne threaded 1/4"-20 holeOptional Flat Surface Adapters Really Right Stuff Multi-Clamp with Flat Surface Adapters RRS-9000441