These are the famous FROG LEGS SHOCK ABSORBING FORKS. When the caster wheel hits a bump the fork is hinged so it will retract compressing a polymer pad for a smooth ride. It definitely helps get over obstacles to reduces spasms. These are for manual wheelchairs only. The standard is black anodized and for a user that weighs 160 lbs. or less. If the user weight exceeds 160 lbs. add HD to your order and the forks will come with a heavier polymer to compensate for the weight. These forks are designed for 3",4",5" & 6" Caster wheels with a 1" hub length. Kit comes with axles and stem nut. These are sold in pairs.