The M-140 Carrier is self guiding with the flanged wheel design. The rollers are made of Delrin, an engineered plastic with excellent properties for use as bearings. The steel axle is machined to a 30 micron finish for smooth rolling under load. The 1.5" long body is made of 1/8" thick 6061T-6 aluminum alloy. Safe working load 25 pounds. 3/8" diam hole for attaching s-hook or trim chain. Available in black or aluminum finish. It is 4" from the top of M140 track to the hole for curtain or 1.5" from the bottom of the track to the hole for curtain.