Rock Climbing for Beginners: Placing a Hex
Whilst many experienced climbers have turned away from hexes in favour of camming devices they are still popular with people starting out and winter climbers. Hexes are far cheaper than cams and there are also places where hexes will work better than cams.
There are two really good options to hexes, one is the DMM Torque Nuts and the other is Wild Country Hexcentrics. Both work in similar ways. Just like wires, the rock needs to be solid and the crack ideally needs a slight taper (See the placing wires article for testing the rock or How to Climb Harder).
Hexes use a camming action created by the sling they are on to help wedge them more securely into cracks. Just like wires they need to be seated into cracks. Importantly though when removing them, you need to twist them in the opposite direction and you can often hear them click out of the placement when you do this.