Keep mounting bracket from rotating?
 

I’m trying to figure out a way to keep this single bolt from rotating. I purchased this accessory mounting bracket that seems like a perfect fit to mount my headlight. It would work out great if I could figure out a way to keep it from swinging side to side. A unique problem that I can’t figure out. Any help would be appreciated, thank you.
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Get a shorter bolt?

I guess it might be difficult to understand what is happening or what I’m trying to do, but the bolt length isn’t a problem.

angle bracket narrow enough to fit in the bracket you bought, and then bend it over the rack tube.

how wide is the channel in the bought bracket? Plumber's strap might work... loop it over the rack and then attach it again on the backside...

A Star Washer between the bracket and rack might work, but won't be a great solution...

zip ties in the right places might work...

and some handwork with a Rat tail file might make the bracket conform to the Rack's top tube, as "a pair of tabs"

i'd try the strap over the tube first... any hardware store will have plumbers strap material... it might need trimmed to width, or might have too large of holes in it... use the channel on the backside of the light mount to trap the strap... double up the strap to add strength...
That same hardware store will have Brass, Steel, and aluminum sheets that could be used to make an L-bracket to hook over the top rail and set in the channel on the back of your new mount bar... you'll need some tin snips and a drill/motor. A 2x4 will work as a form to bend the L-bracket...

All good suggestions. Just trying to keep it looking as clean as possible and would rather keep straps off the top of the rack. You might be right about a plumbers strap. The groove in the bracket is 10mm. Here’s a picture of what was intended to be used.

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try a single INTERNAL TOOTHED Star washer first then... 6mm bolt, right? tighten it as tight as you feel is safe,and use a locking nut on the bolt.

Two lights would balance things, reducing vibrational/bounce torque.

personally, i'd use the strap Minoura provided... it can be done, and that is maleable stainless steel, i bet... besides, it's quite thin and will not intrude on your milk crate basket...

Make or buy a donut or short tube that can orient to the face of the rack's "braze- on" and provide a hard face for your adapter.

OR

Use a file to remove the two side rails from the adapter, then file from the top until it squares up between the rack's mount and back rail.

If it were mine, I'd do the second because it'd be more rigid, but I'm good with a file. Otherwise the first is probably fine.

https://www.summitracing.com/parts/v...4aAlj9EALw_wcB

​​​​​​https://www.carbuilder.com/uk/stainl...10mm-pack-of-5

​​​​​​https://www.amazon.com/uxcell-Rigid-.../dp/B07LBR57LD

​​​​​​https://www.racetronix.biz/p/p-clamp...YaAiQlEALw_wcB

Great minds must think alike. I filed the two sides of the braze on that is on the rack and fit the bracket to that. Came back to see what replies there might be and just saw yours. My filing isn’t the best and there is a slight bit of play but it is otherwise very solid. Got lucky…the light just barely fits.

Thanks for the suggestions and replies everyone.
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Start with a 1 inch cube or thereabouts of black plastic - Delrin would be good. Drill centrally for the fixing bolt, then counterbore to clear the mounting boss on the rack. Next drill horizontally to make space for the cross-piece of the rack and cut away the top back edge of the block as required to clear, so the now-top of the block can be tucked against the bottom of the rack cross-piece, while the bottom of the counterbore is snug against the mounting boss. Finally form a ridge on the front to mate with the groove in the lamp bracket, and assemble.
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5200

Wrap the bar with a single wrap of silicon self fusing tape before installing the bracket.

That or spray it with a bit of rino liner, the stuff used in pickup truck beds, and let that set before installing the bracket.

something to add a little friction.