Nails and screws depend on friction between the fastener and the wood to do their job. When you tighten a nut on a bolt, however, you're actually clamping adjoining members together, producing the sturdiest of all joints. All types of bolts require a hole bored through both pieces being joined together. Here's information about installing machine and carriage bolts. For help with toggle bolts and other anchors, see Fastening with Screws, Related Projects.

machine bolt

Machine bolts have hexagonal heads and threads running partway or all the way along the shank. When fastening two pieces of wood together, slip a flat washer onto the bolt and slide the bolt through the holes in both pieces of material. Add another flat washer, then a lock washer. Screw the nut on and tighten it. The flat washer keeps the nut and the bolt head from biting into the wood. The lock washer prevents the nut from coming loose. Use two wrenches to draw the nut down onto the bolt: one to steady the nut, the other to turn the bolt head.

countersunk

To install a machine bolt in a hard-to-get-at place or when you have to countersink the bolt head, use a socket wrench with a socket extension to reach into the recess. Hold the nut with another wrench.

carriage bolt

A carriage bolt has a plain, round head. Insert it into the hole and tap the head flush with the surface. Slip a flat washer, a lock washer, and a nut onto the bolt. Tighten the nut. The square or hexagonal shoulder under the bolt head keeps the bolt from spinning as the nut is tightened. No washer is needed under the head.

The lock washer should keep the bolt from working loose. As added protection, you can thread another nut onto the bolt, snug it against the first, then "jam" the two together by turning them in opposite directions.