Screws are commonly used to fasten pieces of wood to each other in both outdoor and indoor structures, according to Popular Mechanics. You can also fasten wood to metal with special screws intended to hold the pieces together without putting undue pressure on the wood. In most cases, you should use a washer with the screw to help preserve the life of the wood.
Sheet Metal Screws
Sheet metal screws are designed to fasten metal sheets to other items. You need a socket hex head screwdriver to fasten wood to metal with this type of screw. You can also drill this screw into the metal and wood using a socket bit on your drill. Popular Mechanics recommends drilling at maximum speed and using a screw that is slightly longer than the thickness of your materials.
Lag screws are used for fastening metal to wood as well as for fastening pieces of wood to each other. You must first drill a pilot hole in the metal and wood before placing a washer on top of the hole and the lag screw through the washer, metal and wood. Using a washer reduces the amount of pressure on the wood so that it is less likely to crack or break.
Roundhead Bumper Bolts
Roundhead bumper bolts give wood extra support when used to fasten it to metal, according to Mother Earth News. Like lag screws, these bolts require the use of a washer. You must drill all the way through the metal and wood to use this bolt. After drilling, add preservative to the hole before attaching the washer and bolt. Examine bolts for tightness, and retighten as necessary at least once a year.