Olympic Adapter Sleeve (50 mm)Olympic Adapter Sleeve (50 mm) For More Weight on the 25 mm and 30 mm Barbell Bar: Upgrade with the Olympic Adapter Set The Olympic Adapter Sleeve for Dumbbell Bars with 25 mm and 30 mm Diameters With the 50 mm Olympic adapter for dumbbell bars with a black spring lock, you can upgrade a 30 mm and 25 mm dumbbell bar so that it can hold discs with a hole diameter of 50 mm. The 50 mm adapters can be attached to 30 mm and 25 mm diameter barbell bars and