The Rolson security 33 bit set comes in a flexible rubber block casing that fits in the palm of your hand. Each bit is 25mm long and fits a standard 1/4" (6.35mm) Hex drive screwdriver bit holder socket. The TX-Star and hexagonal bits are hollow to allow the security bits to enter the security sockets which have security pins in the middle to prevent tampering. This set is for use with hand and power tools and contains the most commonly used tamper proof keys on hardware today.