support part 1 such ducts being arranged crosswise relative to the direction in which blocks 3 extend bore like ducts 9 have openings communicating with hose piece 13 which may be stretched to form molded part 12 and surrounding the front of edge surface 10 of plate shaped support part 1 whereby the hose piece serves as connection element 11 a spreading element is inserted into hose piece 13 in the present embodiment the spreading element is in the form of bushing 16 which is conically tapered inwardly in an end zone 17 facing support part 1 and at the bottom end 18 ends in an inwardly pointing inner bushing 19 in this way an annuluar conically tapered receiving space 20 is formed between tapered zone 17 and inner bushing 19 in which space the end of a hose extending from the suction system not shown can be clamped suction ducts or bores 24 extend from the working surface through support part 1 to ducts 9 the recessed first surface areas 23 in which suction ducts 24 end are disposed between individual blocks 3 on the bottom surface of support part 1 each suction duct 24 is in the form of a bore or hole in the bottom of space 6 between two blocks 3 and in each case leads to the associated bore like duct 9 during grinding with the grinding material placed on the exposed sides of blocks 3 the grinding dust produced passes into space 6 between two blocks 3 in which a constant flow of air is also present this air flow is produced by the continuously operating suction system this air flow carries along the.