Hardened steel full extension arms roll on ball bearings.. Swivel base allows you to position your tv at any angle.  Easy to install.Standard size is:  15-1/4" wide x 1-3/4" high and extends 13-1/2".  110 lb. load capacity.Heavy duty size is: 12-5/8" wide x 14-1/2" long x 7/8" high and extends 9".  185 lb. load capacity.