Lag Bolt Shield Anchors | Pilot Hole Sizes Chart

Fastening a lag bolt to a masonry base is no easy task. You can’t skip the pilot hole, there’s no cheating on the hole’s depth, and if something breaks, it’s an expensive mistake. Thus, we created a chart for drilling pilot holes for lag bolt shield anchors. While we aren’t masons ourselves, we hope to prevent you from having to call one.

How Do Lag Shield Anchors Work?

Unlike wood and some plastics, concrete and masonry lack the elasticity that allows for certain materials to compress upon impact. As a result, we have to rely on friction alone to secure a fastener. This means that an anchor is required to effectively grip our bolt inside of the hole. Upon drilling the pilot hole, the user will place the shield anchor inside and continue by driving the lag screw into the hole. As it enters, the bolt pushes the shield anchor outward causing it to expand against the pilot hole walls. Once the screw is completely inside, the whole component should have a snug fit.

Concrete vs Masonry Materials

The biggest difference between working with concrete and with masonry is the timing of the material’s shrinkage. After concrete is poured or mortar is applied, the shrinkage occurs slowly over the life of the object. Consequently, overly tight lag bolts will increase the likelihood of the concrete cracking over time. On the other hand, tiles, bricks, & other masonry materials shrink primarily during the firing process. While the shrinkage amount varies by material, most masonry materials maintain dimensional stability after the initial firing.

Shield Anchor Pilot Hole Sizes

Lag Shield Anchor Size	Pilot Hole Drill Bit Size
1/4″	1/2″
5/16″	9/16″
3/8″	5/8″
1/2″	3/4″
5/8″	7/8″
3/4″	1″

If you’re looking to fasten lag screws to wood, we have a better guide for you! Checkout our article, Drilling Pilot Holes for Lag Screws. We’ll run you through the appropriate pilot hole sizes for both hardwoods & softwoods.