Screw conveyors are the most commonly used conveyors. Dimensions of screws are adapted to the given conditions. Coarse fuel requires larger diameter than that of fine fuel.
Screw conveyors are built in a range from 160 to 400 mm diameter. The way of the slope height is also dependent upon the use of screws. Greatly stuffed screws are built partly progressive, so with increasing gradient in the direction of flow. Normal fillings do not require these measures so that a constant diameter is made.