It is equipped with two openings (1, 10) and has an external surface of several stretches of reduced thickness and consistent in each one of its radial cross-sections. It is of flexible material and comprises a bumpy first stretch (5) defined by parallel perimeter grooves (14). It can be used on tools, especially screwdrivers, and facilitates the coupling of the screw head to the screwdriver through one of its openings or optionally through the magnetic attraction exerted by a built-in magnet (8). Likewise, it can be applied to writing tools, such as propelling pencils or ballpoint pens.