This is the brand my father owned. Mine came from a thrift store. I was asked to illustrate the repair of the leg lock mechanism so here it is.
The leg in question did not lock. I gave instructions, but only tried the temporary cardboard fix. Here I take my own advice and use the lid of a Chinese food container to make a new washer for the mechanism. My bet is you can get something at a hardware store that will do the trick, but if you have this at home. the fix is cost and relatively frustration free.
First remove the locking ring – you don’t have to take the leg off to do it, just unscrew it until it slides off the bottom. If you do this with a mechanism that works you should see a plastic split ring inside. The white arrow shows the original position of the ring.
To make a new one, I used the lid of a plastic Chinese food container. I measured the ring and got 5.2 cm long X 1 cm wide. The initial fit was bad (see below, lower right inset) – the gap you see in the original ring needs to be there to allow the mechanism to tighten it around the leg. I trimmed it to 4.8 cm.
The plastic ring needs to go on first (see below, upper left inset). Then the metal ring went on and I tightened it so that the plastic went back into the bottom of the metal ring.
Trial and error taught me that I needed to be careful installing the new part since it doesn’t curve like the original. The first two tries resulted in the plastic getting caught between the two legs (see below, lower left). I held the plastic with my fingers but I imagine you could use tape to hold it in the right place.
This fix worked perfectly – the ring locked the leg tight and withstood me leaning my weight on it. If I were doing this for myself I would make two, because if you need to take the ring off at any time, it might be easier to replace with a new one.
Nick's Knack 