This is a 10-pack of the SPH-1 Optical Post Holder. The SPH-1 is a slimmed-down, low-cost post holder for 1/2 in. (12.7 mm) diameter SP-Series posts. The combination of a 25% reduction in the outer diameter and set-screw post clamping make this SPH post holder the slimmest post holder available today. The SPH posts have clearance holes in the base so they can be attached directly to an optical table or attached to a slotted base like the (M-)PHB-25 or (M-)PHB-50.