What are these bolt receptacles called?

I’m trying to fix my beloved office chair and am at my wit’s end. All I really want to do is to change the cylinder but this one is stuck TIGHT. I’ll keep working on that, but in the meantime, I’m considering replacing the control plate and mechanism. Unfortunately, the hole pattern seems to be unlike any other chair ever. I’m thinking about getting a standard size, drilling new holes and attaching it. What are the things that the bolts screw into called? It looks like they drilled a hole into the plywood base of the chair and then hammered these threaded “things” into them. I might need to order some if I can’t get the cylinder off but I don’t know what they’re called.



Perfect. Thank you!

You’re welcome. Super-useful piece of hardware.

There are also these (same general idea, but they screw into place rather than hammer in):

If the fastener is subject to being pulled, the first type would not be suitable. It would be excellent as a captive bolt on the back of a plywood sheet though.

In end grain, or wherever the bolt does not go through the material, I think the screw-in type, with maybe some glue for extra strength, would be better.

Prior to reading this post several days ago, I had never before heard of pronged T-nuts. Two days ago, I was helping my mother put up some Christmas decorations, and she lamented the broken stakes on some of her yard ornaments. I proclaimed, “Oh, those are put together with pronged T-nuts! I just read about those.” I made new stakes and attached them to her decorations. Today, news articles from MSN keep showing me advertisements for T-nuts from Amazon.

Curse you, interwebs!