For a wheeled container a door threshold is a much bigger obstacle than a flat corridor: the push force needed to get a castor over a step rises quickly with the step height. For a rigid castor pushed horizontally at axle height, a 200 mm castor needs this multiple of the load it carries:
| Threshold | Force, as a multiple of castor load |
|---|---|
| 5 mm | 0.33 |
| 10 mm | 0.48 |
| 20 mm | 0.75 |
| 30 mm | 1.02 |
A plate 200 mm long that turns a 20 mm threshold into a slope brings the same force down to about a tenth of the load. A few millimetres cause no trouble; at three centimetres a plate is a must.
Choose the plate for the heaviest loaded container. Isotec TBX payload is 500 kg for the 410-795 L models and 700 kg for the 900-1500 L models, plus the tare of the unit. A plate not fixed to the floor slides and is more dangerous than the threshold, so pick a model with an edge lip or fixing holes.
Where dozens of crossings a day use one threshold, a portable plate shifts; floor correction or a fixed ramp is the lasting answer. A fixed plate can stop the door closing, so measure the door leaf's swing first. Two-way traffic needs a slope on both sides.
