This slick Pi Zero case has razor sharp tolerances that can only come from numerous iterations. Less than 6mm thick. Walls are 1.6mm for ideal printing with a 0.4mm nozzle. It snaps together snugly, but adding some pan-head screws will provide standoffs to allow air flow over the bottom vents.
UPDATE: v07c Added cutout for changing MicroSD and various other slight improvements.
UPDATE: v08 Added for Pi Zero W compatibility.
UPDATE: v09b Added with 2x20 right-angle headers for easy GPIO connection. Solder 2x20 Right angle header inserted with bottom of connector flush with bottom of board (farther in than typical). After soldering, trim the pins with a flush cutter to prevent them extending through the bottom opening. You can now build/proto with minimal thickness added.
UPDATE: v10a - Top Header hole cut.
UPDATE: v10b - No GPIO access holes, still has bottom vents
UPDATE: v10c - Minimal, no GPIO, vent, or SD holes. Countersunk screw holes on front face.
ThreeForm ULTRA electronics cases at Shapeways
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Prints in about 1/2 hour using 6 grams of material. No raft, support, or brim is needed.