25mm or 50mm?
This size specification refers to the diameter of the weight plate holder. To determine the correct size, measure the hole diameter of your weight plates.
If the diameter is 50-55mm, then 50mm is the correct size. For 25-32mm, 25mm is the correct size. In gyms and strength training rooms, you'll typically find only 50mm weights. However, many home gym or dumbbell owners have 25-30mm weights.
The included clip ensures that the weight is securely held in any case.