You may have encountered these items if you assemble a lot of flat-pack furniture.
They consist of two pieces: a shaft, which is threaded for half its length and which gets screwed into a hole on one piece, such that half the shaft (the unthreaded part) sticks out. And a “nut”, which fits into a hole on an adjacent right-angle piece and grasps the shaft, and which you then turn with a screwdriver to make it hold onto the shaft tightly.
I want to get some of those. What are they called?
They are generally called cam-lock fasteners. They’re a staple (Ha, I kill me!) of do-it-yourself furniture; you can probably order them in replacement hardware sets from furniture companies like Hon or Sauder, but I don’t know of any place that sells them individually.
Personally I prefer cross-threaded dowels like these. They do result in an exposed bolthead (they sell nicely-finished ones in 1/4"x20), but they don’t have a shaft permanently screwed into the wood, just waiting to get caught on something when you piece is disassembled.
Those are also especially good for stuff you’re planning to put together and take apart more than once, because they don’t thread into the wood itself. Wood screws tend to get sloppy over time when assembled and disassembled repeatedly.
Note that the ones described in the OP don’t necessarily involve unscrewing the wood screw portion in order to disassemble and reassemble, but repeated assembly and disassembly will still stress the wood since furniture designs based on them tend to rely on the fact that they’re strongest when the stress is applied in a particular direction and when many are used as a system, as opposed to individually, so as you put the furniture together, bumping one at a time can loosen the threads up and eventually cause them to fail.
Yeah, I didn’t even think that the posts might get removed. Wood screws are really meant to go in just once. For disassembly, you might replace wood screws with bolts and threaded inserts something like these (best inserted, IME, using a bolt and wrench rather than the screwdriver slot).