●Made of aluminum, Groove step pulley, long time and durable use. ●41MM diameter,6mm aperture,16MM Thickness. ●Suitable for 3-5MM PU round belt. ●Commonly used for DIY small drilling machine, milling machine, small unpowered spindle of machine tool. ●Suitable for 6MM optical axis installation, the top screw hole specification on the side of the boss is metric M4, arranged at 90 degrees