This is the plastic slider that runs up the aluminium extrusion of a Black & Decker 3-way ladder.
Mine broke in half making the ladder/steps very unstable.
Measured up the broken one and designed a replacement in RS DesignSpark Mechanical.
Probably best to print in PETG but I printed in PLA at 0.2 100% infill and it came out so well I just fitted it and all is well
The author marked this model as their own original creation.