These are very heavy substantial wheels.
The large wheel diameter is larger at 250mm making it easier to roll over uneven ground. The tyre is high quality elasticated rubber with a hardness of 75 shore A. The wheel centre is nylon, housing a sealed ball bearing for strength and smooth running.
The individual large wheel load capacity is 500kg! Clearly the wheel is over-rated for a mobile step, but it offers massive resistance to abuse, mechanical handling and very rough ground..... You won't break this one! The axle is 25mm bar and is also strengthened where necessary.
The smaller wheel is also larger in diameter at 125mm. It is again elasticated rubber on a nylon cenre with roller bearing.
The individual smaller wheel and castor assembly is rated to 250kg - again a very substantial wheel and castor.