MSP and TSP Series Miniature Posts are precision ground 0.313 in. (7.9 mm) diameter stainless steel with tapped holes in the ends. The MSP posts have 8-32 (M4) tapped holes in both ends but the TSP differs by having a 2-56 (M2) tapped holes in the bottom end of the post. This smaller thread is included for mounting our 1/2-in. Suprema™ mirror mounts (eg. SN050 or SS050 series) or our Tiny™ mirror mounts (eg.987X series). Each post is supplied with a 8-32 (M4) double-ended set screw, so the set screw can be easily removed regardless of which end protrudes. A cross-drilled hole aids in tightening and loosening the posts. The length of the optical post in inches is indicated by the number after the dash in the model number. We offer the following standard versions: MSP-1 , MSP-1.5 , MSP-2 , and MSP-3 as well as TSP-0.75, TSP-1 ,TSP-1.5 , TSP-2 , and TSP-3. For the metric versions you add an M- to the beginning of the model as in M-MSP-1 for example. MSP and TSP Series optical posts are compatible with ourMiniature Slotted-Base Optical Post Holders.