Nails are typically better in shear and faster to install, but have less withdrawal capacity than screws.
No withdrawal capacity is given to nails installed into end grain (such as the end of a 2×4), so don’t rely on such nails for safety or structural support.
Screws do not typically require ‘lead holes’ unless working with very hard wood or near the end of a member’s end grain to prevent splitting.
Tapcons are probably the best small threaded fastener used to attach something to CMU or concrete. Typical diameters are 3/16″ and 1/4″. They require pre-drilling a properly sized hole to accept the tapcon. 3/16″ diameter tapcons require a 5/32″ diameter hole. 1/4″ diameter tapcons require 3/16″ diameter hole. A hammer drill is sometimes needed to drill a hole in hard concrete, but not always. Make sure the hole is deep enough and clean to limit the potential for tapcon breakage when installing.
When installing tapcons, if possible start with 3/16″ diameter tapcon rather than 1/4″. This is because very often the tapcon itself will strip out the hole, particularly when fastening to CMU. Starting with the larger (3/16″) drill bit for a 1/4″ tapcon would leave less options if this happens. Starting with the smaller 5/32″ diameter drill bit for a 3/16″ tapcon will allow the larger 1/4″ tapcon to be used in a stripped 5/32″ hole.
If drilling a concrete floor slab and hit an obstruction, it could be a harder piece of concrete aggregrate or worse, reinforcement steel. A new drill bit and hammer drill may penetrate hard aggregate, but try elsewhere if you hit steel. Post tension slabs should not be drilled without consulting a structural engineer due to the potential for cable damage and its dangerous release.
When drilling an ungrouted CMU wall, remember that the ‘face shell’ of a typical 8″ nominal CMU block is only 1-1/4″ thick. So consider the thickness of all the materials involved (fastened item, drywall, etc.) and calculate the required length of the tapcon correctly so that it just penetrates through the face shell. Some tapcons are not fully threaded and so a long tapcon with only its shank buried in the face shell will be loose and not hold much. Of course, depth is not so important if the wall is grouted solid.
Expansion anchors, sometimes called ‘red heads’, or ‘wedge anchors’, are also used to fasten something to concrete or grouted CMU. They work entirely different than tapcons. Their outside end is threaded, but only to accomodate the final nut. The inside end has a sleeve mechanism that ‘catches’ the bottom of the hole, and tightens as turning the nut starts pulling the anchor out of the hole. Drill and clean a properly sized hole in the concrete, install the wedge anchor, then tighten the nut. If it does not ‘catch’ and just continues to withdraw, strike with a hammer and try again.
Fasteners installed into wet wood, such as the usual pressure treated, will be more difficult to remove after the wood dries. This is true because wood shrinks as it dries. This is especially true with hot dipped galvanized or ring shank nails.
Rubbing a screw or lag bolt over bar soap will make it easier to install and remove.
Lag bolts are best described as large wood screws that require lead holes. The required diameter of this lead hole depends on the density of the wood. Softwood may require as little as 40% of the lag bolt shank diameter. Lead holes in hardwood may need to be as much as 70%.
Straight threaded rods (all-thread) are often used to fasten multiple members together, such as a multi-ply 2x beam. They are also sometimes set with epoxy into holes drilled into concrete or grouted CMU. Shorter rods can be ordered individually, but it is usually cheaper to cut a longer rod to the lengths needed. This has two potential disadvantages. First, the galvanization coating is lost at the cuts, potentially leading to corrosion later on. Second, threading a nut onto a field cut is often difficult, due to threads being damaged by the cut. This can usually be corrected with careful cutting and work with a thin file as needed.
Washers distribute load from a nut onto the fastened material. Oversized washers can be used to ‘clamp’ one member to another, which can provide additional support beyond relying on the bolts acting in shear alone.
