I recently bought a round aftermarket headlight and brackets. The smallest hole on the bracket accepts an M10 bolt, but the hole in the headlight is larger. Would spacers be good to use in this case? Once the bolts are in the light will hold but I'm afraid that vibration will make the light loose.
Without a picture of the problem it is difficult to provide a good answer.
Whatever the mounting arrangment, it should be secure and you are correct that it should not shake loose while riding...especially in the dark.
There is a piece of hardware known as a fender washer.
Perhaps this will help?
I bought a pack of the fender washers you linked. They are too big to fit correctly into the inside of the headlamp housing, however. I'll have to grind them down somehow. How can I go about making the connections as tight as possible so the headlamp doesn't slip while I'm riding? So far I have the bolts, fender washers, and locking nuts.
bump
Loc-tite and lock washers? Or maybe what you could do is drill out the hole on the bracket so it accepts a larger bolt?