approximately 10 mm wide and 2 5 mm deep are spaced apart radial from the edge and from each other at a distance of about 30 mm these grooves 3 may be of different cross sectional shape provided only they give the flexibility referred to below the grooves 3 provide flexibility which permit the outer part of the disc 1 which contacts an obstruction in the movement of the pool cleaner in use to fold progressively along the grooves 3 this further enables the remainder of the disc 1 to remain in operative contact with the surface being cleaned thus the disc 1 flexes easily while retaining a large surface area in contact with the pool surface a symmetrical series of similarly sized grooves 4 are equidistantly spaced apart and extend radially between the outermost of grooves 3 into the space 5 between the central hole 6 in the disc and the innermost circular grooves 3 holes 7 are made through the disc 1 at the inner ends of the radial grooves 4 also holes 8 are made through the intersection of the radial grooves 4 and the outermost groove 3 the holes 7 can be of larger size than holes 8 and may be of oblong or other non circular shape the sizes of the grooves and holes through the disc at the ends or intersection of the grooves may be varied to give different characteristics to the effect of the disc in use further the preferred material of the disc will be a highly wear resistant polyurethane composition which may also be.