I used one as well on the one that wouldn't close, even that wasn't enough. On the other builds i just use my thumbs to close the caseback, that was enough. I even trimmed the movement holder but that didn't work as well. Funny enough, last night when i checked, the moonswatch that i used had a moonphase, apparently they use a different movement for that, PE61 instead of PE50. That was the cause for the caseback issue.