A butt hinge that prints fully assembled: two leaves with alternating knuckles around a pin that is fused to one leaf and free-spinning in the other. No assembly, no support — peel it off the plate, flex it once to crack the seam, and it swings. The number that makes or breaks it is component clearance: the 0.4mm default works on most well-tuned printers; drop to 0.3mm for a tighter, rattle-free joint or raise it toward 0.6mm if your first try fuses solid. Leaf gauge is the thickness of everything (5mm carries real cabinet doors; stay at 3mm+ or the knuckles get fragile), and the knuckle count is always odd so the pin is supported at both ends — more knuckles spread the load, fewer print stronger on small hinges. If you'd rather drive a nail or an M3 bolt through as the pin, switch to the two-piece external-pin mode: the pin is omitted, the shaft is bored to a running fit, and the ends can take a hex counterbore so a nut sits flush. Gussets (linear, circular, or parabolic webs behind each knuckle) are worth turning on for anything load-bearing. Print tip: print it exactly as exported — open and flat — with no support inside the knuckles. The first layer decides the joint: dial in your first-layer squish, because elephant's foot is the #1 cause of a seized hinge. PETG with 4 perimeters makes a hinge you can hang a real door on. Inspired by Rohin Gosling's classic parametric butt hinge.