Tips on using threaded inserts
Shop fixtures and jigs often require the installation of various clamping or adjustment knobs. That's when you'll reach for threaded inserts. Commonly available in sizes from #8-32 (a #8 screw body with 32 threads per inch) to 3/8"-16 (a 3/8" screw body with 16 threads per inch), there are two basic types: thread-in and press-in, shown top right..
Use thread-in inserts in softer woods and plywood where their coarse outside threads cut easily into the surrounding wood. Simply drill a hole sized for the body of the insert, and screw it into place. In very hard woods, such as white oak and maple, or when the insert is close to the edge of a part and screwing it in may split the wood, drill a hole slightly larger than the outside thread diameter, and epoxy the insert in place. To protect the internal threads from epoxy, cover the end of the insert, as shown bottom right.
Press-in inserts, with their barbed exteriors, work well in hard woods, soft woods, and plywood. Drill a hole sized for the body of the insert, and press it into place with a clamp or tap it in with a hammer and a block of wood. For applications in which the clamping action tends to push the insert out of the wood, such as the knobs that tighten down on the drill-press fence extension rods, drill a hole that engages just the tips of the insert barbs and epoxy it in place.