Rigging carabiners, in general, are steel as there is no issue of weight. Steel carabiners are also stronger than the usual aluminium that is used for climbing. The ISC Wizard is the strongest of the lot, this comes in at a whopping 70kN strength. When rigging, screw gate locking is acceptable, also 2 -way Locking carabiners is a little quicker to do use and just as safe.