Castors are used to move heavy objects or structures (scaffolds or trolleys). They consist of a core (often polyamide or steel) and a tire made of a material such as polyurethane or rubber, which determines its load capacity, durability, and resistance.
The specification of the 3302 PPB series wheels is:
POLYAMIDE WHEEL WITH PLAIN BEARING
Brake F04 - Single plastic brake F18 - Double metal brake