Hex Lag Screw Stainless Steel: Hex Lag Screws are designed to be used in wood or with a lag shield in concrete. They have wide spaced threads for engaging into wood and a gimlet point on the starting end of the screw. It is recommended that you pre-drill a hole into the wood using a slightly smaller diameter so you have proper engagement. The length of the screw is measured from under the head. 18.8 Stainless Steel Hex Lags are for use in exterior, treated lumber and have superior corrosion resistance in all environments.