This “J” Thumb Rest is designed for use on a Fender American Standard Jazz Bass ("J" Bass) and allows you to rest your thumb comfortably for string plucking. It aids in establishing a consistent reference position for your hand when plucking the bass strings. It mounts using 2 of the original pickguard screws. I have provided a picture with reference dimensions for you to check and see if your pickguard screw pattern is useable without drilling new holes (Not Advised). I have also included files for a “No Holes” version if you want to mount it on a pickguard using double stick tape or a plastic rated adhesive. There are many variants of the Jazz Bass and they are produced in several different countries so the version WITH holes will not fit every application perfectly.