Hex Lag Screw Zinc: 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. Zinc Coated Hex Lags are recommended for non-corrosive environments.