FASTENERS 101™
Bolt FAQ

Bolts are fasteners engineered to be used with nuts to hold materials together.

There are many varieties of bolts for wood. Carriage bolts and lag bolts are engineered for use with wood.

You can shop Bolts right here.

The standard bolt measurement includes the thread diameter, thread pitch, and length.

Bolt-preload refers to tightening a bolt before weight or stress is added to the assembly. Bolt pre-load ensures that the bolt will not absorb all of the load, and that it will be spread evenly through the materials.

Tightening a bolt against two objects before adding weight to the material allows the bolt to disperse the weight.

Bolt removal tools use left-hand drilling to extract in two steps. Step one, drill into the bolt head to create a pilot hole for the extractor. Step two, insert the extractor bit that spins in the reverse direction of the threading to spin the bolt loose.

Bolts with flat heads are measured from the top of the head to the bottom of the thread. All other bolts are measured from the bottom of the head to the end of the thread. Bolt length is always measured from under the head to the tip except on flat head varieties where they are measured from the top of the head to the tip.

Bolts without heads are called Set Screws or Grub Screws.

The type of bolt you need will depend on the items you are connecting (e.g., materials, size, diameter, environment).

The numbers and letters on a bolt may be the manufacturer markings and/or the grade of the material.

A carriage bolt, also known as a coach bolt, is a large, strong bolt with an unthreaded square under the head used in wood.

The diameter, thread pitch, and length determine the size of a bolt.

A lag bolt is a large, partially threaded screw, typically with a hex head, that has excellent retention in wood.

An anchor bolt must be inserted into a pre-drilled hole with a hammer and then tightened against an object. This will cause the anchor to expand and lock in place.

A lag bolt is installed by drilling a hole into wood and then driving the screw in with a socket or wrench.

Bolt grades (e.g., Grade 2, 5, 8) indicate the strength and material quality, with higher grades offering greater tensile strength. Check manufacturer specs for load ratings.

Yes, stainless steel bolts, especially grades like 18-8 or 316, are highly corrosion-resistant, making them ideal for outdoor or marine environments.

Use a torque wrench to apply the recommended torque value, ensuring even pressure and avoiding over-tightening which can strip threads.

High-strength bolts, such as Grade 8 or alloy steel bolts, are among the strongest, suitable for heavy-duty applications.

Bolts can sometimes be reused if undamaged, but for critical applications (e.g., structural), it’s best to use new bolts to ensure safety.