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. It has a 3/8" diameter hole for attaching an s-hook or trim chain. It is 4" from the top of the M140 track to the hole for a curtain or 1.5" from the bottom of the track to the hole for a curtain.