Q: When I use my pneumatic nailer, I’m not sure how much nail/brad depth is sufficient to securely hold two pieces together. How do you calculate the gauge/length versus the thickness of the wood to ensure secure attachment?
A: A good rule of thumb is to use nails that are three times as long as the thickness of material you are joining. For example, if you are securing a 3/4"-thick board, you would want to use a 2-1⁄4" length fastener. If the thickness of the substrate to which you are fastening your board won’t allow for this length of fastener, simply add the thicknesses of the two boards you are securing together and then subtract 1/4" to allow for countersinking.
A general guideline for fastener gauge would be to use a 15- or 16-gauge fastener with 5/8" thick or greater stock, an 18-gauge fastener for 1/4"- to 5/8"-thick stock and a 23-gauge pin for stock a 1/4" thick or less. Typically the lower the gauge, the better the holding power, but this larger fastener can sometimes cause splitting — dependent on how close the fastener is to the edge of the board and the species of the wood itself. The best thing to do is to run a trial with some scrap pieces of wood to determine what size works best.