A steel sheet metal crow foot wrench made to fit the v2.0 and v3.0 4003 end caps.
Pictured is v2.0 end cap w/ wrench on it. It fits the v3.0 just the same, so I didn’t bother taking a new picture.
The added radius is usually enough to use this directly in the palm of your hand. But, it also has a square hole for use with a 3/8 drive breaker bar if you really want to get manly with it (not recommended, but there in case you need it). If you smear an ever-so-slight dab of oil/spit/sweat on the o-ring, it goes on super-easy.
I wanted to make the end-caps as light and low-profile as possible. Needless extra weight in your pack is an unwelcome thing. There was no way to get around needing a special tool for this. “Special tool” usually means “overpriced bullshit.” So, I tried to keep this as simple, cheap and practical as I could. It’s a bit of a compromise. While this thing can be a bit clumsy to use with the breaker bar on it, it’s cheap and gets the job done as long as you’re careful about force vector deflection and have some dexterity. It’s a very close tolerance fit absent clearance a wrench would usually have, so that helps you out a bit.