Flush Mount Keyhole Screw Adapter System

FLUSH MOUNT SCREW ADAPTER SYSTEM

A fully customizable 3D-printable wall mounting system that converts standard drywall screws into a flush-mount keyhole system. Inspired by Nest temperature sensor's mounting design, that has a proprietary screw.

OVERVIEW

This system allows you to mount wall plaques and other objects using common drywall screws with a clean, professional keyhole mounting mechanism. The adapter encases the screw head and provides a protruding post that the plaque slides onto and locks into place, flush with the wall surface. Simpler design than the Nest screw and won't require any supports to print, unless creating extra wide keyholes.

I designed this to add a mounting hole to a project that was meant for mounting to a wall, but did not provide mounting holes.  And rather than have to guess how deep to mount the screw for a snug, secure fit, this provides a fool proof and more secure flush mount.

WHAT'S INCLUDED

• screw_mount_adapter.scad - The wall-mounted adapter that encases your screw

• plaque_test_block.scad - A test block to verify fit before modifying plaque

• keyhole_subtraction.scad - Keyhole geometry for boolean subtraction

• config.scad - Central configuration file for all measurements

QUICK START

1. MEASURE YOUR SCREW

You'll need to measure:

• Screw shaft diameter (the threaded part) - typically 3.5mm for #6 screws

• Screw head diameter (at widest point) - typically 8.5mm for bulge head

• Screw head depth (how tall the bulge is) - typically 4.5mm

2. CONFIGURE

Edit config.scad and enter your measurements:

  screw_shaft_diameter = 3.5; // Your screw's shaft diameter

  screw_head_diameter = 8.5; // Your screw's head diameter

  screw_head_depth = 4.5; // Your screw's head depth

  head_cone_expansion = 2.5; // Adjust if screw doesn't fit

3. TEST PRINT

• Open and render screw_mount_adapter.scad → Export as STL

• Open and render plaque_test_block.scad → Export as STL

• Print both parts

• Test the fit:

  • Install adapter on wall with your drywall screw

  • Slide test block onto adapter through wide part of keyhole

  • Slide down to lock into the narrow slot

4. ADJUST IF NEEDED

If the fit isn't perfect, adjust these values in config.scad:

• head_cone_expansion - If screw head doesn't fit, increase this value

• base_clearance - If plaque is too tight on base (default: 0.3mm)

• extension_clearance - If plaque too tight on extension (default: 0.2mm)

5. ADD TO YOUR PROJECT

OPTION A - OpenSCAD (Recommended):

Download all .scad files to the same folder, then create a new .scad file:

include <config.scad>

include <keyhole_subtraction.scad>

difference() {

import("your_project.stl");

// Add keyhole slots at desired positions

translate([x1, y1, z1]) keyhole_slot();

translate([x2, y2, z2]) keyhole_slot();

}

The include statements will automatically load all your measurements from config.scad and the keyhole geometry. Just position the slots where needed!

OPTION B - Using another CAD tool:

1. Render keyhole_subtraction.scad in OpenSCAD → Export as STL

2. Import your project STL into your CAD tool

3. Import the keyhole_subtraction.stl

4. Position keyhole object(s) where you want mounting points

5. Use boolean subtraction/difference operation

6. Export final STL

      NOTE: All .scad files must be in the same directory for includes to work.

TESTED WITH

• 6 x 1-1/4 in. self-drill Zinc plated drywall screws

• Bulge head #2 Phillips

• Head diameter: 8.5mm

• Shaft diameter: 3.5mm

• Head depth: 4.5mm

CONFIGURATION PARAMETERS

See config.scad for detailed parameter descriptions. Key adjustable values:

TIPS

• Print the test block first before modifying your actual plaque

• The adapter should print with the base (wide part) ON the build plate

• The test block should print with the keyhole side facing DOWN for best results

• Do NOT use supports for the keyhole slot (unless creating an extreme size keyhole)

• If using different screw types, measure carefully and adjust config.scad

LICENSE

This design is released to the public domain. Feel free to modify, share, and use commercially.

CREDITS

Designed for standard drywall screws as an alternative to proprietary mounting systems.