Many G1 modellers who have their own rolling stock use the 'Really Useful' brand of plastic boxes, particularly the 22l version for transporting and storing G1 coaches.
A problem with these boxes is that if stacked and then slid over one another the standard blue polypropylene lid clips can come dislodged. If one is not careful one can find that trying to lift 2 boxes just results in lifting one and a lid.
The object of this clip design is to provide a more secure clip that does not project above the box top and prevents dislodging.

A secondary benefit is that boxes can have colour coded clips enabling quick owner identification at crowded G1 gatherings

Printing in PETG G is recommended.

Addition 16-09-23:
Each clip requires two m3 x10mm socket head cap screws as pivots. The .3mf file has the m3 thread modelled but a run through with m3 tap may be required.
The clips have integral dowels to make use of the 'tie wrap holes' in the box ends for additional location and retention.