At last, a really good replacement for O ring mounts supplied on so many bike lights.
Shown here on the 3000 lumen Fluxient 3x XM-L U2 light:

It comes in two parts, the lower part attaching to the bars (standard or oversize) with an allen bolt, the part attached to the light having a quick release.
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It has a limited swivel action to allow the beam away from oncoming traffic:

Currently Fluxient only supply the mount with their light, but it looks like a great mount to me and I'm sure they could supply a quantity to anyone wanting to sell the mount only.