The S-Locks "Silent Feature": No more rattling in combination with S-Locks Strap Buttons, Locks and Lock-Wheels. new and unique one-piece construction, easy to install via 3 mm (1/8") Allen key. special 4 mm wood thread in S-Lock size M for maximum grip. Optionally available in sizes S (3.5 mm) and L (4.5 mm). Please refer to the installation instructions in the description below for size specifications. hardest steel for maximum wear resistance and safety. including high-grade felt washers to protect your instrument.