I can figure out most things for myself, sometimes with a little help from Google. But this was a puzzler.
BMX hub on a road wheel. I wanted to remove the cog to try another size. The lock or retaining ring has two notches and comes off counterclockwise. You need to restrain the freewheel, typically with a chain whip. With the chain in place, there's no room for this tool
to grab on. I couldn't find one of these
which fits; the
Park FR-2 is too small. I had an idea that a pin spanner might do the trick, but wasn't sure there would be enough leverage.
There wasn't. However, with some duct
tape (good enough for airplanes!
or not) and a piece of wood, eureka:
Thank you Archimedes.