Castor ultra low of very high quality in fiber nylon. The load capacity is particularly high for a model of this diameter as you can load up to 1800 kg on 4 units (steel thickness of 4 mm on the plate). The material allows for increased resistance to static loads over the long term (so no crushing or permanent deformation is to be expected). 2 ball bearings are present inside the wheel to limit the effort at the start of the wheel.
Its second advantage is its very low bulk which only exceeds the narrowest edge of the plate by 2 mm. You can therefore install them under industrial machines without the mount hitting the feet of the technicians.