Hipshot Ultralite Bass Xtender 3/8 Y Key Gold
Extend the range of your bass with the Ultralite Xtender Key - instantly drop your E string to any note from E to low C with a flick if the lever. Ultralite version perfectly matches Gold Ultralite tuners.
This is the 3/8 model (diameter of stringpost) and is designed to fit 9/16 headstock holes. 'Y' Style tuning key.
Here's the installation insrtruction PDF