Lag bolts, also called lag screws, are large wood screws with hexagonal heads that are perfect for projects like mounting your new flat screen TV in your house. While using heavy-duty lag bolts for hanging your TV might be overkill, there are some things that you really don’t want falling and that’s where we love lag bolts.
Generally, Lag screws are used to connect something semi-permanently to wood after predrilling the pilot hole into the securing wood beam. Driving lag bolts is easy to do with an impact driver or wrench, but care needs to be taken for the final torquing of the bolt as its not uncommon to pop the heads due to over tightening of the bolts and that’s a quick way to ruin your afternoon.
Lag bolts have a sharp gimlet point and coarse threads for maximum holding force in wood, but due to their large diameter must be predrilled. Extra care must be taken to make sure the pilot holes are in the center of the stud and that the predrilling is to the depth the entire screw will eventually be.
What are lag bolts used for:- Roof beams
- Garage pillars
- TV wall mounting
- Heavy construction
- 1/4” lag bolt - 2.0 inch embedded depth, 272 lbs. sheer
- 5/16” lag bolt - 2.5 inch embedded depth, 368 lbs. sheer
- 3/8” lag bolt - 3.0 inch embedded depth, 432 lbs. sheer
- 1/2” lag bolt - 3.0 inch embedded depth, 624 lbs. sheer
- Threads must be embedded in the side grain and must be located in the middle third of the structural member for maximum strength.
- Read full article for particulars including links at bottom of page.
Lag Pull-out force*
- for a 5/16" lag bolt, pull out force is between 205 - 307 lbs per inch threaded depth, depending on the wood choice used.
- Threads must be embedded in the side grain and must be located in the middle third of the structural member for maximum strength.
- Read full article for particulars including links at bottom of page.
- Lengths is from the under-head bearing surface to the extreme tip of the screw
- Diameter is the width of the major thread diameter or untreaded shoulder of the screw
- Steel 60,000 psi minimum
- Stainless Steel 100,000 psi minimum (18-8 stainless steel)
- Hammer the center punch in the middle of the broken bolt so drill bit will have a starting point.
- Drill a pilot hole and using a specialty extraction bit proceed to SLOWLY and in reverse, drill the bit into the pilot hole. It may be helpful to gently tap the drill containing the extraction bit into the pilot hole with a light hammer tap before attempting to drill. If all goes well, continue reversing until bolt is removed or you can get some vice grip pliers onto the bolt to remove it fully.
* How much bolts can hold in depends on many factors including, but not limited to, wood type, threaded depth, load angle. Full technical data from American Wood Council can be found here: - AWC Calculator found here, Kinetics Data for lag screws