Annoyingly, the screw-to-wall tabs on my brand-new tool rack broke off whilst I was installing it. To fix, I cut slots in front of where the old tabs had been, and slotted in these 'tool rack tabs'.

Tab width = 15mm. Tab shoulder = 40mm. Make sure your slot is significantly narrower than the tab shoulder.

UPDATE: Added .SCAD file + customizer option (my first crack at customizer - I hope I did it right...)