These clickers fit piercing holes that are 1.6 mm in size, but with the help of an adapter they can also be adapted to piercing holes with a larger diameter.
The measurements 6.3 mm and 7.9 mm respectively in the product description refer to the height of the jewelry. If you are unsure, a good tip is to measure with a regular BCR; if an 8 mm BCR is tight, it may be time to invest in the larger variant. All clickers are 1.6 mm thick.