Diameter: 3/8 Length: 1-1/4 Material: Stainless Steel Head Style: Hex (9/16 Wrench) Point Type: Gimlet Thread Length: Partial Hardness: 18-8 Type: Hex Lag Screw A lag screw is similar to a wood screw but generally is much larger with a hexagonal head. Lag bolts are designed for securely fastening heavy timbers to one another or to fasten wood to masonry or concrete.