EDIT: Okay, errand done. So here are the two legs.

Tab A goes into slot B

Like so

A more distant view

Two things to notice here. One is that the legs are pretty close together. I did that so the 16" disc would fit on top. And so it would barely clear the outside of a propane tank, for storage. A five gallon tank will fit neatly under the legs. Wouldn't cook with it there, just store.
The second thing is the slight angle cut in the top of the legs, matching the slope of the disc. Both the 16" and the 21" fit nicely on top. I couldn't decide if I wanted a ring, or flat bits of steel, or what, for the disc to rest on. This seems to work.
Were I to do over, I'd spread the legs further apart, for stability, and because a 16" disc is really small.

Tab A goes into slot B

Like so

A more distant view

Two things to notice here. One is that the legs are pretty close together. I did that so the 16" disc would fit on top. And so it would barely clear the outside of a propane tank, for storage. A five gallon tank will fit neatly under the legs. Wouldn't cook with it there, just store.
The second thing is the slight angle cut in the top of the legs, matching the slope of the disc. Both the 16" and the 21" fit nicely on top. I couldn't decide if I wanted a ring, or flat bits of steel, or what, for the disc to rest on. This seems to work.
Were I to do over, I'd spread the legs further apart, for stability, and because a 16" disc is really small.