L.H. Dottie TBC363 3/16'' x 3'' Phillips/Slotted Mushroom Head Toggle Bolt. Toggle Bolts, or butterfly anchors, are a light to medium duty anchor intended to be used in hollow block, wallboard, plaster, plywood, and other hollow base materials. Once fully opened, Toggle Bolts significantly expand the surface area making contact with the back of the hollow wall. This spreads out the load of the fastened object, increasing the weight that can be secured. The maximum weight a Toggle Bolt supports, depends on the size of the bolt and the thickness of the substrate. To accommodate the Toggle, installation requires a relatively large hole compared to other types of hollow wall anchors.