How to Tell the Difference Between E and H Bends

The terms "E" and "H" plane refers to the electrical and magnetic planes of rectangular waveguide. The electrical plane or E-plane is the narrow plane of the waveguide and the magnetic plane or H-plane of the waveguide is the wide plane.

A simple way to remember this is that an E-bend is the "easy" way to bend waveguide and an H-bend is the "hard" way to bend waveguide.