The soft aluminium crush washer on Monster 1000 S4R fills this microscopic gap. When you tighten the drain plug to the specified torque, the washer compresses (crushes) permanently, conforming exactly to the contours of both mating surfaces.
FEBI 39733 OIL DRAIN PLUG WASHER SEAL RING DIN 7603 14.4x19.8x2 5PCS A4912
Copper Oil Drain Plug Washer O-ring Assortment (Genuine Neilsen CT4093)
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