K5S40 Standard 0-1/4” Beginner Cleco Sheet Metal Fastener Kit w/ Mesh Carry Bag. The K5S40 Cleco Fastener Set offers the best value. These spring-loaded and steel bodied fasteners are dedicated to light clamping forces (No more than 25lbs.). Cleco fasteners are a simple, plier-actuated, inexpensive, alternative to competitive fasteners. A cleco fastener (sometimes spelled cleko) is also known as a skin pin. Cleco fasteners are widely used in the manufacture and repair of aluminium-skinned aircraft and in automotive repair. Cleco fasteners are used to temporarily fasten multiple sheets of material together before the pieces are permanently joined.