Every heel tip has a metal pin attached with it that is inserted into the hole of the shoe heel. From the outside of your shoe heel, there is no way to figure out which size of metal pin will fit in. There are three most common sizes of metal pin in any shoe – 2.5 mm (Small), 2.9 mm (Medium) and 3.04 mm (Large) and one of them will fit the heel hole of your shoe. If you received heel tips with only one size of metal pin, there is only a 33% chance that it will fit your shoe heel properly. We therefore provide you 3 pairs of heel tips, each with a different size of metal pin.