The helicoid and the catenoid are parts of a family of helicoid-catenoid minimal surfaces. It again, similarly to a simple catenoid, separates two branches. Classic examples include the catenoid, helicoid and Enneper surface. The catenoid and the helicoid are two very different-looking surfaces. The radii of rings and the height of catenoid are equal to 1.0. Soap film attached to twin circular rings will take the shape of a catenoid. It began with Euler's proposition of new figure, called "catenoid". These are the plane, cylinder, sphere, the catenoid, the unduloid and nodoid. There is a catenoid of idempotents in the split-quaternion ring. In differential geometry, a "k"-noid is a minimal surface with "k" catenoid openings. The catenoid is obtained by rotating a catenary about its directrix.