The tiny sandblaster turns out to be a Badger 260 with miniature Propel threaded fittings on the air line:
Foreseeing a Propel washer getting lost in the confusion, I punched a few from a cork sheet and trimmed them to half-thickness. The little brass hole punch isn’t good for more than a few whacks, but that’s all I needed. My cork is crumblier than theirs, but I got a few decent-looking washers and, with a bit of luck, won’t need any of them.
Maybe I should make a soft gasket from a thin plastic sheet?