GO2 SOCKET | OFFICIAL WEB SITE
It is $14.99 with free shipping to the United States and $10 to ship anywhere else the U.S. Postal service delivers. The full list is here:
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This is the one 20mm socket depicted. I thought that it was a set, eleven sockets from 10- to 20mm, but it simply adjusts down to 10mm.
I thought you would often not be able to get a 10mm Go2Socket where you need it, but a 20mm G2S for a 10mm nut or bolt? Not likely!
This is where I learned about them:
I ordered one.