Professional model makers are in the business of building (and sometimes designing) one-of-a-kind creations. Very occasionally, though, a model maker decides that fabricating a particular part from scratch is not in the best interest of the project. In these instances, an existing product might be bought and deconstructed to extract a commodity out (sometimes referred to as “kit bashing”).
These plastic wheels have been removed and reassembled from off-the-shelf toy trucks. They will be added to built-from-scratch trucks. The trucks themselves are not the main focus of the finished model. Ultimately this project will be a training model for a shipping company that would like to have table top practice at the real life task of loading and unloading pallets.
It’s uncommon to find preexisting parts, particularly in the right scale, for a custom model project. Internet searching has made it a bit easier to find a usable commodity. Sometimes it’s a smart choice for a project, and ultimately for the client’s budget, to include ready-made pieces in the construction.