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 DMM Zodiac aluminium is an excellent rigging carabiner if you want to keep the weight issue minimal, this comes in at a whopping 32kN strength. When rigging, screw gate locking is acceptable, also 2 -way Locking carabiners is a little quicker to do use and just as safe.