The sizing of the clips works as follows:
- C451 size - fits 19mm diameter mic
- NT5 size - fits 20mm diameter mic
- KM184 size - fits 22mm diameter mic
If you don't have a micrometer to measure the diameter you can always use a string and wrap it around the part where you would put the clip and mark its length. Lay this string out and measure it's circumference (C).
Diameter = C/3.14
You want to size the clip on the tight side. ie if it is 21mm use the NT5 clip size not the KM184. The clips will stretch and accomodate up to about 1.5mm (larger) in size but will be tight.