The D'Addario Flex Lock strap blocks provide simple yet secure protection against accidental strap release. Designed for guitar and bass, these clever locks get the job done without tools or permanent modifications. Inspired by the classic Grolsch bottle cap solution, they attach easily to strap buttons for a low-profile look. The Flex Lock strap blocks let you safeguard your prized possession and focus on your music. Just press them onto your instrument's strap buttons by hand—no tools needed. Their tight grip keeps your strap firmly in place so you can rock out without worries. The Flex Lock blocks attach and remove in seconds, whenever you want to swap straps. No more frustrating strap malfunctions or invasive installations. The D'Addario Flex Lock strap blocks work with most standard straps and instruments. Their clever spring-style mechanism adjusts to fit 1/4" or 3/8" strap buttons securely. Electric guitars, acoustic guitars, bass guitars and more are all covered. The Flex Lock blocks' flexibility makes them easy to use with your existing gear. Simply squeeze on and enjoy reliable protection. With broad compatibility, these blocks let you reinforce your instrument strap setup without limitations.