5/16" Inch Ball Bearing with 1/8" diameter integrated 1/8" Inch (3.18mm) Pin Diameter 1/8" x 5/16" x 1/2" Inch 5/16" inch (7.94mm) Ball Bearing with 1/8" inch (3.18mm) diameter integrated 1/2" inch (12.7mm) Long Axle, Pin Diameter is 1/8" inch, Bearing Outer diameter is 5/16" Inch (7.94mm), and Width of the assembly is 1/2" Inch (12.7mm Long), Bearing is made of Chrome Steel.