These clamps are constructed of 304 SS with the adjusment screws being zinc plated steel or stainless steel. The adjustment screw is a 3/8" hex size.
The smallest clamps are great for coolant connections, where the larger clamps are utilized on charge piping and hoses for intercooled turbo and supercharger applications. Be sure to measure the outside diameter of your hose to select the proper clamps, not the size of the pipe as hose is typically 1/4" (6mm) thicker per wall than the pipe (1/2" or 13mm total). Below is a general guideline for clamp selection, but may not necessarily be accurate for all applicatoins. If you are unsure, measure the outside of your hose when it is installed on the pipe with a pair of calipers. If you do not have calipers, measure around the outside of the hose on the pipe with string and a tape measure, then divide the result by pi (3.14):