Lag bolts serve a variety of purposes, with a main purpose being to handle structural applications that are going to be under considerable stress as these bolts are capable of handling heavy loads. Different size bolts are used depending on the amount of stress the bolt will be under. While it is advisable to use bolts that are structurally rated, there are resources available that follow ASTM guidelines to determine load capacity based on the bolt diameter. It is important to follow code regulations to ensure that the bolts used are capable of meeting required load bearing capacity.
Lag bolts require a few steps for use that include pre-drilling holes with multiple diameters. For example, when fastening a deck ledger, a lag bolt requires a clearance hole through the ledger board and a pilot hole through the rim joist. In addition, it is important to include a washer when using lag bolts as these add additional weight bearing strength. It is not possible to counter sink lag bolts, which means that using certain drivers like an impact driver can result in over-driving the bolt by driving the washer into the wood.