The Saris Bones Knob is the OEM replacement knob for the Saris Bones 2 and the Bones 3 bike racks.
Perfect replacement, my Bones is like new! got a couple extra just in case I need them in the future. the set from ACK was cheaper than the Saris site, and shipping was super fast.
The originals will wear out over time. These are great and cheap to have on hand, throw a couple in your glovebox and you will be set if one strips out.