O ring that sits in the small channel of the divertor body underneath the cap. Common problems requiring the replacement of this o ring is leaking water around the divertor when the pumps are running. The temptation is to over-tighten the cap (ultimately breaking the cap). Over-tightening causes the o ring to flatten and to lose it's sealing properties...
Seats on the underside of the divertor top or the shaft of the divertor rotor. Fits both 1" and 2" divertors and there are x2 that sit on the square spline of the rotor.