What is the name of those thingies?

[Brian Kent]

It is the thing you screw into a board that will hold another screw firmly.

I have a dining table used every week by 3/4 ton of gamers. The legs need some major bracing and I want to screw some of these into the bottom of the table so they can hold screws from the braces.

Clear as mud? It is in my brain, too.

[Roy Petersen]

Threaded inserts?
https://en.wikipedia.org/wiki/Threaded_insert

[Brian Kent]

Threaded inserts?
https://en.wikipedia.org/wiki/Threaded_insert

Thank you. That is it exactly.

[David Eisenhauer]

Have to imagine the usual characters such as Woodcraft, Rockler's, etc sell these.

[Dave Cav]

McMaster Carr will have a good selection of them and they'll arrive practically as soon as you hang up the phone/press the "submit" button.

If the fastener will not be visible, a T-nut will also work and they're a LOT easier to use than threaded inserts.

[Davis Young]

I live less than 30 minutes away from a McMaster Carr center so I usually order will call. I have often clicked the submit order button and then immediately driven over there. I have yet to beat their order pickers.

[Lee Schierer]

Be aware that threaded inserts for wood are different than those that are used in metal. The ones for wood have much thinner exterior threads designed to cut into the wood.

[Larry Edgerton]

I use the metal ones, but I take one and cut a groove in it so it acts like a tap and first cut the threads with that one, then insert the one that will stay.