Machine for the spray application of products on discontinuous flexible laminar elements with an extended surface, in particular for the painting of tannery hides comprising: - a spray booth for applying dye to the surface of said hides by means of spraying means; - a drying oven for said hides after the spraying treatment; - a conveyor belt for said hides comprising a plurality of flexible cords parallel to each other and spaced apart which define a support surface on which said hides are spread out; - motorization means to drive said conveyor belt and said hides resting thereon through said spray booth and through said drying oven; - at least one grooved shaft (1; 100; 200) placed transversely to said conveyor belt at least between the outlet of said spray booth and the inlet of said drying oven to keep said flexible cords parallel to each other and spaced apart during their forward movement, said grooved shaft (1; 100; 200) comprising a cylindrical body which extends mainly along a longitudinal axis and externally to which there are a plurality of coaxial radial annular discs one after another along said longitudinal axis which define a plurality of radial annular grooves between them each of which is delimited: - by two of said radial annular discs adjacent to each other, each having the radial annular wall facing inwards with respect to said radial annular groove; - by the outer annular perimeter edges of each of said radial annular discs; - by an annular bottom belonging to said cylindrical body and connected to each of said radial annular walls by means of an annular connecting zone belonging to said cylindrical body, characterized in that in said grooved shaft (1; 100; 200) each of said radial annular walls extends between the starting point of said annular connecting zone and the starting point of the outer annular surface which perimetrically delimits said outer annular perimeter edge and faces the outside of said radial annular groove, wherein in at least one of said radial annular grooves on said radial annular walls at least two intermediate points (9a; 29a; 59a) are defined in which the distance (9b; 29b; 59b) between said at least two intermediate points (9a; 29a; 59a), measured along a straight line parallel to the direction defined by said longitudinal axis, and the maximum distance between said radial annular walls, measured at said starting points of said outer annular surfaces which perimetrically delimit said outer annular perimeter edges, also measured according to a straight line parallel to the same direction defined by said longitudinal axis, are related to each other by the following relation: 9 b; 29 b; 59 b ≤ 6 a − 1 millimeter in which said distances (9b, 29b, 59b, 6a) are expressed in millimeters. - a spray booth for applying dye to the surface of said hides by means of spraying means; - a drying oven for said hides after the spraying treatment; - a conveyor belt for said hides comprising a plurality of flexible cords parallel to each other and spaced apart which define a support surface on which said hides are spread out; - motorization means to drive said conveyor belt and said hides resting thereon through said spray booth and through said drying oven; - at least one grooved shaft (1; 100; 200) placed transversely to said conveyor belt at least between the outlet of said spray booth and the inlet of said drying oven to keep said flexible cords parallel to each other and spaced apart during their forward movement, said grooved shaft (1; 100; 200) comprising a cylindrical body which extends mainly along a longitudinal axis and externally to which there are a plurality of coaxial radial annular discs one after another along said longitudinal axis which define a plurality of radial annular grooves between them each of which is delimited: - by two of said radial annular discs adjacent to each other, each having the radial annular wall facing inwards with respect to said radial annular groove; - by the outer annular perimeter edges of each of said radial annular discs; - by an annular bottom belonging to said cylindrical body and connected to each of said radial annular walls by means of an annular connecting zone belonging to said cylindrical body, - by two of said radial annular discs adjacent to each other, each having the radial annular wall facing inwards with respect to said radial annular groove; - by the outer annular perimeter edges of each of said radial annular discs; - by an annular bottom belonging to said cylindrical body and connected to each of said radial annular walls by means of an annular connecting zone belonging to said cylindrical body,