This pack of four Ernie Ball Strap Blocks securely fastens your strap to any instrument, they fit over most strap button types and provides a tight fit without any modification to your guitar. Made of flexible, durable rubber that will slip over the strap button after the strap is installed to provide a very secure connection and a simple, effective way of keeping the strap from coming off the strap button. The pack of four contains 2 x red and 2 x black blocks which is enough for two complete guitars.