A lag screw, also known as a lag bolt, is a fastener that has a hex head, and external hex drive, and coarse threads that extend a minimum two-thirds of the shaft length. It can have right or left-hand threads. A lag screw is used to fasten wood to wood, in applications where strength is required. It can be used with a washer to prevent wood splintering, and a wrench for tightening and loosening. It is typically made of steel, stainless steel, or galvanized steel. It can be hot dipped and galvanized, and may have zinc or other coating. A lag screw may meet standards, such as American Society for Testing Materials (ASTM) B18.21, American Society of Mechanical Engineers (ASME) F593 or A153, and American Iron and Steel Institute (AISI) 1006-1022.