These are available in two formats, round spring and s-spring. These terms are derived from the configuration of the spring in the socket part (B part or female part). S-springs were the original fasteners and are still most popular, due to their tight closing action.
Round spring are the later innovation and this less expensive option - popular in all trades. These fasteners are all available in a range of colours, sizes and finishes as well as steel or brass-based metals. Remember that although steel is cheaper it can RUST.
All these are available with the customer's own logo on the cap.