A small correction...

The individual "trays" or boxes is part of their Assorter series. They are made with either fixed compartments or the 55 model which allows for the interchangeable inserts.

The HandyBox is the name just for the rack that fits 4 Assorter 55s.

It also looks like they've changed the naming of some of their inserts for the Assorter 55 and inserts are now available with trays that group them together.

Raaco also makes interchangeable inserts for the Assorter 27 which is shallower or the Assorter 80 model which is deeper but are not compatible with the HandyBox carrier.