Antistatic suction hoses in 36 and 50 mm. Dry dust moving through a plastic tube builds a static charge, which at best gives you a shock at the nozzle and at worst is a genuine hazard around solvents. An antistatic hose conducts it away. The larger diameters are for volume — a planer or a chop saw rather than a sander.
Compare products and choose the right one for your work.