Thumb Caddy is an inch long, U shaped plastic device wrapped in soft rubber that clips onto the thinnest part of the shaft and slides up onto the middle of the grip. The Thumb Caddy is then aligned with the club face. The device creates a concave crevice for placing your thumb into when gripping the club. This device aims to keep your grip consistent throughout the swing by keeping the thumb position constant. Greater consistency in grip and club face alignment will give you a greater chance at producing a consistent swing motion.
Click here for more info: Thumb Caddy

Thumb Caddy