Only the advent of nuts in the beginning of the 1970s allowed Clean Climbing to become an established climbing style of its own. Nuts are passive protection gear and are put into cracks which narrow in the direction of a potential fall (mostly downwards!). But first of all, you need to find these cracks. Well placed and in the right spot, nuts can hold hard falls. Just like when using slings on rock jags, you need to take care that the rope drag doesn’t pull the nut out of the crack. The characteristic “pling” when that happens is known by all clean climbers and normally leads to your hair standing on end, especially if it was the last nut right before the crux, in which you are now hanging.
Really small micro-nuts are hard to place and bearly hold a lead fall. To be honest, you mostly don’t even take them with you to avoid the temptation of using them as trustworthy protection.
How to use?
Nuts can be placed in all cracks that narrow in fall direction. The rock needs to be solid, as a fall causes huge forces on the sidewalls (blasting forces of over a ton!). Nuts behind loose flakes are useless and might only cause additional rock fall.
The nut should have a large contact surface with the rock and should be placed already in fall direction. Further it should be pulled tight so it does not move when you continue climbing. If it is the last nut before the crux, it is possible to use light hammer hits to make sure it doesn’t come out. Of course, this will cause your following partner to curse and it’s also not really an anti-aging treatment for the nut. It is often enough to extend the nut with several quick-draws or a sling to keep it from coming out.