A compact and efficient stop for establishing the position of maximum extension in a mechanical joint, which comprises a free-floating piston, a piston-retaining pin, and a resilient bumper positioned to engage one end of the piston. The piston, retaining pin, and bumper are located on one side of the joint. A cross stop bushing on the opposing side of the mechanical joint is positioned to engage the exposed end of the piston when the joint is in its position of maximum extension. Applications may include, but are not limited to, use in orthotic and prosthetic devices wherein a larger tolerance in the range of motion is provided for a locking mechanism to engage as the joint reaches maximum extension, while any unwanted feeling of free movement in the joint at full extension is concurrently dampened. A secondary advantage is a softer extension stop for a user.