The Hex-Nut (KH) series clecos are operated with a pneumatic power tool and best suited to high-production settings requiring fast, consistent, uniform clamping force. Its ‘free-wheeling’ design allows it to back completely off while still remaining intact.What are Cleco fasteners? Cleco fasteners are speciality fasteners made for industrial design. Clecos, or skin pins as they are sometimes called, are made of metal, and require a great deal of compression pressure to properly fasten. Cleco Fasteners are generally used to bind two sheets of metal together in a secure fashion prior to riveting or welding.