referring to fig1 and 2 , a slide ( 2 ) is secured to a carrier ( 1 ). the carrier ( 1 ) is provided with , for example , casters ( 3 ). a shaft 12 receives a stack of letters b , and has as a bottom , slide 2 . the slide ( 2 ) extends in a helical shape , with a plurality of curves encircling a vertical helical axis ( a ). the shaft 12 is defined laterally by an outside wall ( 4 ) and an inside wall ( 5 ). a transfer point ( 6 ) is joined at the upper end of the slide ( 2 ). a transfer point ( 7 ) is formed at the lower end of the slide ( 2 ). the transfer points ( 6 , 7 ) can selectively serve to feed - in or feed - out the letters . the transfer parts ( 6 , 7 ) extend approximately horizontally and tangentially to the helical shape of the slide ( 2 ). in the embodiment according to fig2 the slide ( 2 ) is outwardly inclined in the radial direction with respect to the helical axis ( a ). correspondingly , the outside wall ( 4 ) and the inside wall ( 5 ) stand at a diagonal . because of this inclination , letters ( b ) slide i . e . to the outside , to the outside wall ( 4 ), on slide ( 2 ), which aligns their front edges . a number of postal items , for example 3000 letters , may be accommodated in a space - saving manner in the transport unit . the transport unit can be easily transported , for example rolled from one station to another in a mail - sorting or distribution facility , or conveyed in a mail car . in fig3 the transport unit is shown set up with sorting compartments ( a , b , c ). letters are pushed manually , one after the other , out of the respective compartments ( a , b , c ) and onto slide ( 2 ) via the upper transfer point ( 6 ). once a sorting compartment is emptied , the transport unit is rolled to the next sorting compartment , whose letters can then likewise be pushed onto the slide ( 2 ). in this stage , the lower transfer point ( 7 ) is typically closed . so that the letters can be moved mechanically on the slide ( 2 ), the transport unit includes a conveying apparatus ( see fig4 and fig5 ). fig4 shows the slide ( 2 ) and the conveying apparatus separated from one another with in the axial direction . the conveying apparatus according to fig4 has a sleeve ( 8 ), which forms the outside wall ( 4 ) of the shaft 12 . the sleeve ( 8 ) is coaxial to the helical axis ( a ), and can rotate about the helical axis ( a ) on carrier ( 1 ) using a motor m not shown in detail . the sleeve ( 8 ) has a slot ( 9 ) which extends approximately vertically over the height of the slide ( 2 ), and in which a sliding plate ( 10 ) is seated to be displaceable in height . the sliding plate ( 10 ) projects radially over the slide ( 2 ) and into the shaft slide ( 2 ) forms , which receives the stack of letters . if the sleeve ( 8 ) rotates in the direction of the arrow ( r or l ), the sliding plate ( 10 ) is then correspondingly carried along . simultaneously , sliding plate ( 10 ) slides upwardly on the slide ( 2 ) in the direction of the arrow ( o ), or downwardly in the direction of the arrow ( u ). depending on the direction of rotation , the sliding plate ( 10 ) pushes the stack of letters lying on the stationary slide ( 2 ) either upwardly toward the transfer point ( 6 ), or downwardly toward the transfer point ( 7 ). an unloading or loading of the shaft of the transport unit is thus possible . in the conveying apparatus according to fig5 a cylindrical inside part ( 11 ), which is coaxial to the helical axis ( a ) and forms the inside wall ( 5 ), is provided . the inside part ( 11 ) is seated on the carrier ( 1 ), and can rotate in the direction ( r ) or direction ( 1 ), relative to the stationary slide ( 2 ), using a motor not shown in detail . in this case , the outside wall ( 4 ) is fixed against relative rotation with respect to the stationary slide ( 2 ). the slot ( 9 &# 39 ;) in which the sliding plate ( 10 &# 39 ;) is vertically displaceable is found on the inside part ( 11 ). during the rotation of the inside part ( 11 ), the stack of letters is conveyed , as described , upwardly or downwardly by the sliding plate ( 10 ).