The most reliable and hassle-free instrument strap lock system ever devised. No need to remove or replace existing strap buttons on your guitar; just slip easily installed Strap Blocks over the existing strap buttons and that's it-you're ready to go, with your strap locked securely in place.Strap Blocks work with most OEM strap buttons, and are available in convenient four-packs containing one black pair and one red pair.