Over the years, I've bought many IKEA Terje foldable chairs. It's a popular model.
However, they quickly get "wobbly". I think the problem is with the joints (although I'm not sure). Any ideas on how to tighten them... I actually think it's not possible to tighten them...
You'd need to re-squeeze the rivets, which is likely impractical, or just temporary respite.
An alternative may be to replace the rivets with nuts & bolts - though if you're stripping the joints that far, it would probably be better to also re-line the holes, as they will be expanding due to the off-axis movement occasioned by the loosening of the original rivets.
Maybe something like small dome or countersunk barrel nuts could do the job - & be less prone to snagging on things.
Images search, for multiple examples - https://duckduckgo.com/?q=sunk+barrel+nuts&t=osx&iax=images&ia=images
Those fasteners are rivets. You can tighten them up by placing the smooth end on an anvil or other very hard surface and hit the other end with a large nail set and hammer. The problem with this is it's not a long term fix since the wood has been ground down a bit and you can only compress the rivet so much.
A more durable fix would be to grind the rivets off with a rotary tool and get some nuts, bolts and washers and re assembly the chairs. You can repair any ground down wood with expoy or wood filler.
