This kit includes 3/8 inch (10mm) Acme thread press rod sized for headset installation, a pair of interchangeable Liner Quick Handles, a quickaction 3/8 Zipnut, and a full complement of the most common guide sizes to ensure efficient and accurate headset installation Utilizes the same 29 degree angle Acme thread design found in high precision applications such lead screw drives for CNC machines This design results in wider and broader thread bases which have greater strength and overall durability This thread design is much more accurate than standard V shaped threads, providing exact 90 degree force for perfect bearing seating and installation alignment