The drop-in anchor is also called concrete drop-in anchor, concrete drop-in, mini drop-in. It consists of two parts: a zinc plated steel tubular expansion shield and a solid, cone-shaped expander plug in tubular expansion shield. The expander plug is hardened and tempered to prevent galling. On the bottom of expansion shield, there are four equally placed slots. The top of the anchor shield is smooth and the bottom part is sometimes knurled. The use of the bottom lip is to allow maximum depth and holding power. Drop-in anchors are made of zinc plated steel, 304 or 316 stainless steel. The anchor is used in solid concrete only. When the plug is pushed into the bottom of the anchor with a setting tool , the anchor will expand in the hole and it's kept by friction.