Part: clip — printed open, 180 mm long: the lower jaw (90 x 20 x 3.2) and the upper jaw (84 x 20 x 2.4) end to end with a 0.5 mm mechanisms.living_hinge_web between them. Fold the upper jaw over: a half-round rib along the lower jaw (mechanisms.snap_ridge) presses the bag into a matching channel in the upper jaw (mechanisms.snap_groove, 0.3 mm wider for the film), and the upper jaw's tip snaps under a lip on the catch block at the lower jaw's end. The upper jaw is the spring: pushing its tip down the lip's 45 deg ramp bows it, and it springs into the 0.8 mm undercut. To open, push a thumb into the scoop at the tip toward the hinge and lift. Two 10 x 2 mm disc magnets glued into pockets in the underside hold it on the fridge door.

Print flat as built, PETG (the living hinge is validated in PETG and TPU; PLA fatigue-cracks within tens of folds). Fold once while the print is still warm. Declared hinged: the 0.5 mm web is the design, not a thin-wall defect. The catch block's undercut is a 0.8 mm deep, 2.8 mm tall horizontal slot in a vertical face: it bridges without support.

Assumptions (user unavailable): sized for a 20 mm jaw and a ~2.4 mm bow-to-snap; magnets 10 x 2 (use MAGNET_H = 3 and JAW_T_LOW = 4.4 for 10 x 3); no text on the jaws.