Snap-on's LTAM2124 is 4mm thick with open end 21mm & 24mm. Not sure you would want to grind a mm off a $36 wrench, but it's an option--especially if you can get the crankarm to come out a mm.
Steve Barner, bought one like it for French BB's many moons ago and it's still shiny, Bolton, Vermont
> Date: Wed, 11 Jun 2003 07:12:05 -0700
\r?\n> From: Jan Heine <heine@mindspring.com>
\r?\n> To: classicrendezvous@bikelist.org
\r?\n> Subject: [CR]Source for 21 mm cone wrench?
\r?\n> Message-ID: <a05010407bb0ce891e277@[66.167.139.148]>
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\r?\n> Message: 17
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\r?\n> Listmembers,
\r?\n>
\r?\n> I need a thin 21 mm wrench. Doesn't need to be quite as thin as a
\r?\n> cone wrench. It's for a locknut on a BB spindle, so it must fit
\r?\n> between the BB shell and the outer locknut. I'd say 3 mm max.
\r?\n> thickness.
\r?\n>
\r?\n> Looking through the VAR catalog, I see 22 mm and up for BBs, and up
\r?\n> to 18 mm cone wrenches.
\r?\n>
\r?\n> I know Park makes a 20 mm cone wrench. But no 21s!
\r?\n>
\r?\n> I guess I could buy a standard 21 mm wrench (if available - my
\r?\n> wrenches skip that size and go from 20 to 22 mm!), and grind it
\r?\n> thinner.
\r?\n>
\r?\n> Thanks for your help.
\r?\n>
\r?\n> Jan Heine, Seattle