English to Spanish Tech/Engineering Mechanics / Mech Engineering

No entiendo a qué se refiere con *hexagonal flats* y es díficil para mí ya que no hay una ilustración con el manual que traduzco que me pueda ayudar. El texto es el siguiente:

----------------------------------------

1.Lock out air supply to unit.
2.Remove cylinder from clevis on the cover and bottom.
3.Unscrew the cap on the rod end of the cylinder by turning the *****HEXAGONAL FLATS***** on it. This will allow you to pull out the piston and access the internal o-ring seals.
4.Unscrew the bottom end of the cylinder with a wrench. This will provide access to the o-ring on the bottom.

--------------------------

Gracias