Earphone Foam Earpads
There are 3 sizes of Foam Earpads for Earphones and Earbuds
Most earphones use a 17mm size earpad, and the front of the earpiece is size about the same size as a Dime Coin. If you can place a dime against the face of the earpiece and it is fairly close to that size of the earpiece, then the 17mm foam earpads (D-10 and D-10-20) should be the ones to fit your earpiece.
If your earpiece seems larger, and is more like the size of a Penny coin, then you will find that the 20mm earphone foam earpads will be the ones to order. Part number D-20MM is a bag of 100 replacement earpads, and the D-20MM-20 is a bag of 20 replacement 20mm Foam Earpads.
If your earpiece is even larger, more like the size of a Nickel coin, then you will want to order the DFEP100 or DFEP20 foam earpads.