Tech Tip: Installing Lag Screws
Lag screws are made of unhardened steel (or stainless steel, which is also unhardened, but is stronger than the mild steel used in standard lags). That means that lag bolts are soft, and can easily be over-torqued and broken during installation. Worse yet, if such a thing is possible, is that many users mistakenly think that because of their size compared to standard screws, lag screws do not need pilot holes. Unfortunately, the wedging action of a large-diameter lag screw will quickly split most lumber! For best results, drill a pilot hole for the threads, and a clearance hole for the shank. I generally drill the pilot hole through both pieces at one time for alignment, then enlarge the pilot hole to the clearance hole size in the piece being fastened .
| Lag Bolt |
Pilot Hole |
Preferred Clear. Hole |
Loose Cl. Hole |
Tight Cl. Hole |
| 1/4" |
3/16" |
15/64" |
1/4" |
7/32" |
| 5/16" |
7/32" |
5/16" |
21/64" |
19/64" |
| 3/8" |
9/32" |
23/64" |
3/8" |
11/32" |
| 1/2" |
3/8" |
31/64" |
1/2" |
15/32" |
18-8 Stainless Steel vs. Hot-Dip Galvanized
Stainless Steel lag bolts are typically made of 18-8 grade stainless which offers good corrosion resistance and machines easily. They may stain if used in a seaside environment but are acceptable fasteners when used with ACQ pressure-treated material. Unlike many competing products, McFeely's stainless bolts are passivated so thay may even be used below the waterline without fear of severe corrosion and eventual failure.
Hot-dip Galvanized bolts have been the standard for heavy-duty applictions for many years! Our hot-dip galvanized bolts have a minimum tensile strength of 60,000 PSI and conform to either ANSI/ASME B18.5 (carriage bolts) or ANSI/ASME B18.2.1 (lag screws and hex-head cap screws)