Large-diameter wheels with pneumatic or solid rubber tyres for site work, since they roll over cable, rubble and thresholds. Small hard castors suit smooth warehouse and workshop floors only - on a construction site they jam on debris and drop into gaps. This is the specification most often regretted after purchase.

Up to the manufacturer's stated limit, but the practical constraint is stability when the trolley is tilted onto two wheels to cross a threshold or a kerb. A stack that is stable upright can overbalance when tilted, so the usable height is usually lower than the weight rating alone suggests.

Often not - stability usually limits the load before weight does. A trolley rated for a high load may become unwieldy well below it once the stack is tall, particularly on uneven ground. Assess the combination of height and weight you will actually move rather than the headline figure.

It lets the handle be set to a comfortable height for the user and the stack, so a tall load is balanced rather than fought. A fixed low handle on a tall stack forces an awkward posture and makes the load harder to control, particularly going down a ramp or over a kerb.

Where work regularly involves buildings without lifts, yes - moving a loaded stack up stairs by hand is slow and a genuine injury risk. Powered stair climbers are heavy and expensive, so they suit repeated use rather than occasional. For flat-site work they add cost and weight for nothing.

Some convert to a flat platform or accept straps for general loads, which stops the trolley being single-purpose. Where the trolley top is purely a latching interface, it will only carry system boxes - worth checking if it is expected to double as general site transport.

On a proper system trolley it latches, using the same interface as the boxes, so the stack and trolley move as one and cannot separate when tilted or wheeled over rough ground. A trolley that merely supports the stack is considerably less secure and is not equivalent.