SET 6 MOLDS (foto2) FOR CASTING OF CONCRETE WEIGHT PLATES (BARBELL DISKS) . 
1 pcs: 2.76 lb (1.25kg), Ø 162мм; thickness 30 mm 1 pcs: 5.51 lb (2.5kg), Ø 203мм; thickness 42 mm 1 pcs: 11.02 lb (5kg), Ø 268мм; thickness 48 mm 1 pcs: 22.05 lb (10kg), Ø 351мм; thickness 54 mm 1 pcs: 33.07 lb (15kg), Ø 397мм; thickness 60 mm 1 pcs: 44.09 lb (20kg), Ø 400мм; thickness 90 mm 
These molds you can get a lot of concrete disks for barbell having spent for not much money 
For each mold listed approximate weight, due to the fact that the specific weight of concrete is different. Weight on the molds specified in kg Molds are made of ABS plastic thickness 1,9-2 mm.Depending on the geometry of the product wall thickness can form less than the above dimensions. 
To form a hole for the metal bar, you need to attach a piece of pipe the diameter of the metal bar (photo 4) and fill it with concrete. When concrete become solid you can cut away this with a thin knife. Foam aren't supplying, because it unknown what diameter of metal bar you using. With this molds you can get a lot of cheap concrete disks for barbell.