Coulter patented several different geometries that work with the Coulter Principle. (Image from US Patent #2,656,508)
<a href="https://en.wikipedia.org/wiki/User:Mnrhyner" class="extiw" title="en:User:Mnrhyner">Mnrhyner</a>
2012-08-09
<a class="external free" href="https://en.wikipedia.org/wiki/File:Coulter_geometries.jpg">http://en.wikipedia.org/wiki/File:Coulter_geometries.jpg</a>