Captive Nut Join

Captive Nut Joint is the strongest bolted joint you can put in a printed part without inserts or tapped plastic: a hexagonal pocket that traps a standard hex nut, and a coaxial clearance hole so the screw comes in from the other side and threads straight into it. Because the pocket stops the nut turning and its shoulder takes the load, you tighten from one side with no wrench on the back — and the joint can be undone and redone as often as you like, because the thread is steel, not plastic. Pick a size from M2 to M10 and it sets both halves from the same standard: the ISO 273 clearance hole and the nut pocket sized from the real across-flats and thickness of an ISO 4032 nut. By default you pick the nut face and the screw enters the opposite one; turn Flip on to pick the screw face instead, and the pocket moves to the far side with the entry chamfer following you. Nut pocket clearance (0.15 mm per side by default, the printable drop-in sweet spot) tunes how snugly the nut goes in, Nut seat sinks it a little deeper than the pocket floor, and Bolt-entry chamfer breaks the screw-side edge at 45 degrees. Print with the pocket mouth facing up: the nut pocket bridges cleanly over the clearance hole below it, so the whole joint comes out without support. Make sure the host is thick enough for the pocket depth plus a floor underneath — a pocket that breaks through leaves the nut with nothing to react against. The nut thickness in the table is ISO 4032; DIN 934 nuts are a touch thinner and seat fine, and if you want one fully recessed, raise the seat depth. If your pockets print tight, raise the clearance a few hundredths rather than filing the nut.