A simple but fully parameterized 90° L-bracket designed in OpenSCAD. 

Both arms have countersunk through-holes (countersinks face the inside of the L, where the screw heads sit), a small 45° chamfer at the inside corner for reinforcement, and every outer edge is rounded so the printed part is comfortable to handle. Open the .scad file in OpenSCAD and use the Customizer (View > Customize) to dial in arm length, plate thickness, hole diameter, countersink size, hole offset, inside-corner chamfer size, and edge-rounding radius - all in millimeters. Default values give a ~25 × 25 × 20 mm bracket suitable for M4 wood screws. 

Prints flat on the horizontal arm, no supports needed.

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