So, to get the best hex nut capture socket fit, I wrote a parametric OpenSCAD script to produce a simple test part. Any screw size with either a hex head or a round capped head can be configured to produce a test part for 3d printing. Use the Thingiverse Customizer to produce custom STL files. The project with variable setting details are published here: http://airtripper.com/1594/hex-nut-capture-socket-sizing-for-3d-printingFull instruction are here: http://airtripper.com/1594/hex-nut-capture-socket-sizing-for-3d-printing Download the OpenSCAD file or use the Thingiverse Customiser to get the required STL files you need. // - Select part to view/print from list view_part = 1; // [0:design, 1:head_up, 2:head_down, 3:horizontal] // - Screw head diameter - flat side to flat side on hex nut or bolt head head = 6.75; // - Screw head type - [6] for hex head and [50] or more for round head type = 6; // - Screw size diameter size = 3.65; // - Screw size diameter smoothness smoothness = 50; // - Screw size length - not including screw head length = 5; // - Screw head length cap = 3; // - Block border thickness between screw head and block edge border = 4; // - Print layer thickness - only required for head down print layer = 0.25;