OnTrackYou Discs have a 2" (50.6mm) diameter center hole. This is beneficial as they fit all commercial bars and most plate loaded gym equipment ranges.
Available in 2.5kg, 5kg, 10kg, 15kg, 20kg, and 25kg variations
Weight plates may incorporate holes for ease of carrying (called "grip plates") or be solid discs (especially those used for competition).
National, International And Olympic Level Competitive Weight Plate.