Co-Built lock nuts

Because dirt track race bikes have tyres that can run in both directions all a racer has to do to get a new racing edge is to take the wheel out, turn it around and put it back on. But rather than taking the tyre off the rim someone, a long time ago, came up with the idea of quick release sprocket and discs.

A big knock-off nut (shown in the lower of the top two photos) screws down onto the sprocket (or disc) and is tightened or removed by an equally big spanner. But Jan-Willem of the Dutch Brothers came up with a design and the Co-Built fellas made it. A C-spanner tightens up the ring and an Allen key tightens it to secure it in position. It means you don't have to swing on a huge spanner to lock it down. A neat solution.
£25 a pair at Co-Built