Puzzled about splines on ceramic cartridges

[bigpapanoodle]

I need to replace the ceramic cartridge on a Franke Triflow kitchen tap. I have counted the splines on the uppermost part of the cartridge and I make it to be 21. Most of the cartridges I see for sale state 20 splines. I have counted the teeth time and time again and still make it 21! Am I dealing with an obselete format or is there something else I'm missing here?

 

[johnnyplumb]

you managed to get to 21, best i've got to is about 4 :devilish:
best to contact franke themselves Spares & Servicing