Basics of Stoppers
Stoppers are a type of Passive Protection
and are also known as Nuts. Stoppers are designed to be crammed deep in small to medium sized cracks. Most stopper placements are only appropriate for one direction of pull (normally down).
When placing nuts, the key is to have as much surface area of the nut touching the rock as possible. If the nut is relying primarily on a small crystal on one side you risk having that crystal break, which in turn allows the nut to be released from the rock. An ideal nut placement is often a crack that starts wider than the nut you plan to use and gradually narrows until the crack is thinner than the actual nut. Therefore you can place the nut in the wide section and pull down until the nut becomes 'stuck'.Full Article