Solution to minimize overall height and maximize load capacity. Dual wheel casters also improve stability and swivel more easily than wider-face single wheels. However, this 40mm diameter caster is the most "ugly" one of the Series.
Pneumatic tire absorbs chock on uneven floor by cushion of compressed air. Absolutely recommended for hospital, resort, hospital, labs, outdoor, etc. However, price is steep: 2 - 3 times higher than the domestic solid rubber one.