face of the disc which provides flexibility for the outer part of the disc to fold progressively along the grooves application_number US 93570701 A description the disc 1 illustrated is moulded from suitable plastics material usually polyurethane the disc 1 is generally of the size of the discs referred to earlier in this specification and may have 400 mm and 105 mm outer and inner diameter respectively the outer edge 2 of the disc 1 is scalloped as shown and the edge rounded the side of the disc which is not shown in the drawing is that which in use is remote from the surface being cleaned a series of upwardly projecting fins extending a short distance towards the centre of the disc and equally spaced around the periphery will preferably be provided on the disc grooves 3 which may be made 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.