Adjustable-Height Wood and Metal Stool

The best way to attach the legs to the base block is 1-1/2" pocket holes from underneath with 2-1/2" pocket screws and glue. Confirm the outside-to-outside measurement of the legs matches the plan so the splay is right.

This is the harder part. Notch the cross supports with a table saw or circular saw so the all-thread can pass through the center of the base. It's some work, but it's the right balance of effort and a clean result.

Attach the cross supports to the legs with 3" screws or lag bolts. Do NOT fasten the two cross supports to each other — the all-thread has to pass through the center between them.

Cut the seat round from a 2x12 or 1x12 with a jigsaw (or use a bought plywood round), attach the floor flange to its center, and thread the all-thread into the flange with pipe-thread tape for grip. Thread the assembly into the base with nuts and washers.

Turn the seat to raise or lower it. Once you've set the height, make sure the nuts are still tight so the seat can't slowly unwind under weight. Sand and finish the wood.