I have a 2012 M37 with 114k miles, I've had it since 05/07/2018 and am the second owner--but it's been a Florida car it's whole life. Last year I found the 21 mm OEM lug wrench was a very tight fit on the lug nuts; then last month I picked up a nail in the right rear tire--and found 21 mm (both the OEM lug wrench and and a 21 mm hex impact socket) were a complete no-go--I had to use a 22 mm socket (In which the nuts jammed and had to be driven out) to get the tire off. Measuring the nuts I found they were all 21.8+ mm across the flats.
As many will know the lug nuts are 3-piece assemblies: the nut itself, a captive washer and a crimped on covering to make them look like acorn nuts--they are NOT, but are rather just plain ol' through-drilled hex nuts--which can be machined much faster and hence cost less to make (see photo below).
The crimped "faux-acorn nut" cover appears to be thin gauge (0.75 mm) stainless; the actual nut measures 19.8 mm across the flats for a total assembled 20.55 mm across the flats.
The problem is that over time vibration and corrosion take their toll and the assembly "swells" to well over the 21 mm lug nut spec (as stated above mine were all 21.8+ mm.
The solution was simple , new 21 mm REAL acorn nuts. The good news is that I got a nice set of 20 from Amazon for just $19.45 (w/ free shipping for Prime members):
If you shop elsewhere note that they are an M12x1.25 thread, and if used with OEM wheels must have the captive washers used on hub-centric factory alloy wheels. DO NOT use conical seating nuts with the OEM wheels--they may damage the wheel and jam it onto the wheel studs!
That's it, just thought I'd share my photo and affordable solution.
FWIW I have since found that both Toyota and Ford have had similar issues with fake "acorn" lug nuts...
