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
- SM57 size - 31mm 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
The clips fit pretty securely and will fit up to about 1.5mm max above their rated size. That being said there is a lot of leeway in terms of which clip you use. Some people particularly if the mic has a mat surface prefer to go to the next larger size and don't seem to have any issue with the grip strength or the fit. So if you have 21mm you could go smaller to the NT which would work fine but are tight or to the KM size which still seems to have plenty of grip. A lot of people seem to prefer the larger size as they are easier to fit on and the plastic is like the lego plastic and may cause some micro abrasion which would be reduced with the larger mic clip.
My clip seems to small when I measure it and I am afraid I might break the clip?
Some people think that the clips are like a normal microphone stand clip and the mic will slide in so the clip must be slightly larger than the microphone at rest. This is not the way they work at all. The curve of the sides is such that when under tension they accommodate a microphone of the design dimensions while applying enough force to be able to carry the weight of the mic and a similar mic and its cable.
The NT 5 mic clip is perfect for a 20mm mic but will stretch for up to a 21mm microphone. The mic's snap into the clip. Some people get a little freaked out by the fact that they require a fair amount of force to push them on but they would not be able to support the microphones if they were not this way.
If you don't feel comfortable using a mic clip that snaps on like these are designed to you certainly could return them and we would refund you your money. We have worked with a few people that think the clips will break if snapped on but they won't. They are made of the same material that Lego's is made out of and are pretty well indestructible. If you break them while putting them on a microphone of the correct size we would just replace them.