Metal toggle bolt consists of two consists of two parts - Zinc Plated Steel Bolt and two spring-action snaps wings. So metal toggle bolt is also called butter anchor. When the wings open to spread load out over a greater surface than other anchors. Metal toggle bolt is designed to use in hollow base material such as hollow concrete blocks and drywall. It need a pre-drilled hole. Our steel toggle bolts are offered in 3/16", 1/4", 3/8" and 1/2" diameters, and each diameter has 3" and 4" length. The butterfly anchor diameter is refer to the diameter of the bolt that fits into the toggle bolt, and also the hole diameter needed.