How can I re-tighten the lever locks on my light stand?

I don't know whether they're all the same size, but my aging Manfrotto tripod takes an 8mm standard hex-nut 'wrench' socket. Available from any DIY store, for a buck/pound/euro or two. You probably have one in your toolshed already.

It feels very slightly loose, but perfectly effective. It may be actually an old Imperial or US size rather than metric, but 8mm fits just fine.

From comments - It seems larger sets, on ⅜" or ½" shafts might be too heavy duty. I tested the above types, on ¼' shaft & on hex-bit shaft quite successfully.

It was most likely tightened originally with a socket wrench, probably one designed for a 1/4" shaft (since these would allow for the thinnest sockets). The best tool for the job is whatever size socket you need and a nut driver (be careful that you don't over tighten!).

But, fix the actual root problem the way your would with any nut that comes loose when it shouldn't:

• Washers
• Blue Loctite or clear nail-polish
• A spring

Most quick release clamps of decent make use a spring on the release tab over the bolt's threads to provide tension and to keep things from loosening up through repeated cycles.

Alternatively, you can replace the clamps with nicer quick release clamps (if you are so inclined).

For a longer-term solution, if this a frequent problem for you, I'd recommend replacing the nuts with nylon lock nuts (which resist loosening due to the nylon friction insert in the nut), and replace the screws with appropriate hex socket cap screws. That way, you can use standard tools (i.e., Allen keys) to tighten the screws if they ever loosen from the nylon nuts.

Note that cap head socket screws have a smaller diameter head than their equivalent hex crown bolt head. In order to maintain sufficient bearing surface to the plastic below the head, you might need an appropriately-sized washer below the socket cap screw.