The M-PPF50 Spring-Loaded Filter mount supports 2.0 in. (50.8 mm) square filters with a thickness of up to 5 mm. Two steel springs hold the filter on a frame with a 1.57 in. (40 mm) clear aperture. Two M-PPF50 filter holders can be screwed to one another to form a unit that holds two filters. This filter holder has an M6 threaded hole for post mounting.