Here's a selection of positive stop grommet nuts. Whenever mounting anything in rubber it's important to ensure the grommet is compressed the ideal amount, too much and the rubber will distort and eventually destruct. Too little and the mounted item will move and vibrate, negating the effect of rubber mounting and also eventually destruct. Not a new idea, the Japanese have been using it for years on their bikes. Particularly helpful when mounting things on bikes prone to vibration, 360 degree twins are a good example. In this selection I turned up on the lathe, the bullet headed one on the right is thread for bolting to a frame tab, used for mounting side panels, the grommet in the side panel just slips over the bullet head in a tightish fit, the front of the panel has two grommets secured by grommet bushes and allen head bolts. Next one is a threaded, positive stop, through nut I used for a similar purpose. The third is a grommet bush with a 6mm through hole, this one is used for mounting the seat. The bush is mounted in the grommet in the seat and an allen head screw passes through the bush and threads into a tab welded to the frame. The last is a grommet bush with a 6mm through hole, turned up from delrin. This one is used for mounting the aluminium battery carrier I welded up. As the battery poles are very close to the side of the carrier, I didn't want it shorting out if a nut, spanner, or whatever, made contact between the battery pole and the carrier, the Delrin bush isolates the carrier from the frame, so if the positive battery pole is shorted across to the carrier, it won't result in the battery shorting out.