fig1 from the rear side edge of the table top 12 which distance a is a measure of the length of the future double hem by changing the measure a for example by displacing the folding device somewhat sidewards the width of the hem is also changed the device functions in the following way a piece of fabric 13 e g a sheet which by appropriate transport means as endless transport bands not shown is transported along the feed table 72 with the fabric edge which is to be hemmed contacting the side edge 73 of the feed table will be inserted under the roll 66 of the first roll pair 64 and gets its continued transport movement by the endless band 50 of the folding device in cooperation with the table top 12 and the shaping rule 51 respectively when the piece of fabric has reached the section line xiv xiv in fig1 the piece of fabric 13 is by the band portion 50d pressed against the table top 12 while the projecting portion 13a of the piece of fabric 13 corresponding to the measure a will hang freely downwards along the free longitudinal side edge of the table top as.