The M-140 Master Carrier is self guiding with the flanged wheel design. The 4 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 5.5" long body is made of 1/8" thick 6061T-6 aluminum alloy. Safe working load 50 pounds. 3 each 3/8" diam holes on 2" centers for attaching s-hooks or trim chains. Attachment holes are 1.5 inches below the bottom of the track, and 4 inches below the top of the track. Available in black or aluminum finish.