Many karabiners, including those sold here, are made of steel, as it is a strong material suited for holding human weight and resistant to wear and tear. Karabiners of other materials exist, but most rigging karasbiners used in arboriculture are steel, where that material is available.
Each karabiner is generally only part of a set, and the karabiners sold here include both two- and three-way karabiners for different forestry purposes. Karabiners of this type can also be used for climbing other natural surfaces such as rock, but these particular karabiners are designed for trees and perform most effectively when used as part of a forestry operation.
They can also be used domestically, with proper training and caution, to trim, mend or cut trees on one's own property, or to help a friend with trees in their garden or on their land. Note again that karabiners alone do not provide proper security to a climber, and other forestry equipment will be necessary.