The SeaStar Teleflex Steering Helm Wheel Mounting Kit includes a washer, key & nut; for attaching steering (helm) wheels to SeaStar (Dometic) 3/4" tapered shaft helms.
The kit includes a large washer, a key which locates into the helm shaft to secure the helm wheel in the correct position and a lock nut to tighten onto the shaft to prevent the helm wheel from pulling off.
If you are buying a new steering helm then the steering wheel mounting kit is usually included. The spare hardware kit is only required if you have lost or dmagaed the key or securing nut.