The Rath Hand Guard trombone hand support is an adjustable all-metal device that allows you to shift the weight of your instrument from the base of your left thumb to the back of your left hand. It attaches to the bell brace and can be adapted to fit most common or standard sized braces. One size fits tenor and bass trombones. The unit is adjustable to fit your particular hand size and instrument setup. Can be self-installed or with the assistance of a repair technician.