. The Service Caster Series #20 is ideal for light and medium duty material handling, carts, equipment, and shop projects. Listing is for a set of four (4) Service Caster Series #20 swivel casters, four (4) swivel 10mm threaded stem casters with top lock brakes, 5â diameter by 1-1/4â wide semi steel cast iron wheels. When searching for a reliable and durable solution to your caster needs, consider Service Casterâs Series 20 sleeve bearing semi-steel cast iron casters.