I’m struggling with these junk 21 mm lug nuts on my Toyota Tacoma. They barely fit, and I have to hammer them on. Anyone got any ideas on how to remove them? 
Maybe try a 7/8 socket, it’s just a bit bigger than a 21 mm. Also, not all 21 mm sockets are the same, so you could try a different one. A 12-sided socket might help too since they tend to fit a little looser.
Yeah, that’s what I was thinking. If you have to hammer the 21 mm on, it could be an SAE size. Worth a shot.
It’s probably just a chrome cap on the lug. I used to work at a Ford dealership, and we’d hammer on the SAE equivalent to get them off. Once you’ve had issues with one or two, the rest will likely give you the same problem soon. Might be time to replace all the lug nuts.
I’ve never dealt with this myself, but you could check out half sizes. Steelman Pro makes a 21.5 mm socket, which might help if the lugs have swollen a bit.
Give your local Ford dealership a call. They’ve dealt with these types of lug nuts for years and can either give you advice or pop them off quickly for you.
Man, I don’t know the answer, but I always wonder if mechanics overtighten these lugs on purpose. Every time I get new tires, I have to break out a huge breaker bar just to get the wheel off. 
Uuga duga, bro. 
This is exactly why I get anxious after my tires have been worked on at a shop. 