Stem Size: 3/8" x 7/8" (10mm x 22mm); Fit for 10mm x 22mm office chairs.The Stem is Smaller than the regular 11mm Stem Caster Wheels. Safe For All Floors; Protect your floors with our soft & strong high grade polyurethane wheels. If you're worried about your office chair scratching up your hardwood floors, fear no more! Our extra large casters are incased with soft clear polyurethane which guarantees to not leave black marks or scratch up any surface. Smooth and Quiet Rolling; Our precision ball bearings combined with vibration reducing polyurethane tires will give you a smooth and silent roll. They roll amazingly on hardwood floors, carpet, tile, concrete, stone or vinyl. Easy to Install; No tools required; Pull out your old office chair casters and push in your new wheels until stem is firmly seated and secure. Warning: The office chair wheels are made of 10mm screw rod. Please measure the valve stem size before purchasing and purchase according to the product parameters. Thank you for your purchase! ! !