What's the difference between active and passive protection, and when should you use nuts, hexes and cams?

By placing gear along the way, through which the rope can be threaded, the lead climber creates anchors to limit the length of fall they could take. However, it must be remembered that the gear is not the only thing affecting how far they could fall. The reaction time of the second (belayer) to hold the rope tight must be added, and finally one must include the stretchiness of the rope and the shock absorbency properties of the system as a whole.

There are two main types of climbing protection:

Passive protection

The simplest type of climbing protection. You wedge it into a crack so that if a load is applied it tightens deeper into the rock. Most wedge-shaped 'nuts' are curved in some way and many also feature a hollowed out mid section to reduce weight and allow placement in less uniformly tapered cracks. Sizes vary from a few millimetres thickness to about 2cm. Hexcentrics, AKA hexes, are another common form of passive protection. They are bigger and, as the name suggests, six-sided. These are useful for bigger, tapering cracks.

Active protection

Camming devices are a form of 'active protection', also known as 'cams' or 'Friends'. A lever on the device can be pulled to close a cam, then you insert it into a crack and release to open it out. They can be used in parallel-sided cracks where protection would otherwise be impossible.

There are pitfalls to using cams, however. The most common failure is that the cams do not bite into the crack. This might be because too small a cam has been used or that the taper of the crack is too great for the cam radius to manage. Always place cams with the stem facing the direction of anticipated load. In smooth-sided cracks cams can 'walk' deeper into the crack as the movement of the rope rocks them to and fro. Always extend them adequately to reduce this leverage.