Our product listing includes a set of four (4) - 3" wheel size stem casters, 2 swivel with brakes and 2 regular swivel casters. Stem size is 5/16"-18 x 1" which is very common on light duty racks, furniture, dollies, stools, carts, and many other light duty institutional equipment and applications. We are offering these casters with one of the highest quality wheels on the market which is a Gray Non-Marking Thermo Engineered Rubber caster which is designed to absorb shock, vibrations, reduce noise, roll over debris, cracks, gaps, and obstacles with ease. The tread is a 75 Shore A Durometer Tread which is much softer than a 95 Shore A polyurethane wheel you would normally see elsewhere. Our tread is softer which adds an extra layer of floor protection as well as protection from shocks for expensive equipment, glass, or electronics when comparing this wheel to a polyurethane wheel. Thermo Plastic Wheels are also known as TPR Wheels, Thermo Wheels, and Thermo Plastic Rubber wheels. These wheels are softer than a standard polyurethane wheel you would normally use. With a 75 Shore A Durometer (Softness of Wheel); these are exclusivley made to roll over debris, gaps, cracks, obstacles with ease. The softer tire allows it to grip and roll-over obstacles opposed to harder wheels that will just push or get stuck while rolling. Applications include: Computer racks, conveyor stands, medical & laboratory equipment, printers, copiers, modular framing enclosures, electronic enclosures, manufacturing machinery and automation enclosures, business & machines, shop equipment, diagnostic equipment, hospitals, pharmaceutical labs, food service, and more!