Screws come in a huge range of types and sizes for an equally vast array of construction tasks. Choosing the wrong screw for the job can split wood or compromise the soundness of a structure. To avoid these problems, contractors need to know the three essential characteristics of a screw: gauge, length and threads per inch (TPI).

The gauge number, listed on the packaging of screws sold in the imperial system, corresponds to a fraction of an inch in diameter. A screw with a #5 gauge is 1/2 of an inch in diameter, while a #8 screw is 3/8 of an inch. The length of a screw is determined by the material it will be used to fasten and its thickness. Generally speaking, a screw should be no more than half as long as the material it is being attached to in order to hold securely. Using too long a screw can result in it splitting or damaging the opposite side of the material.

The threads on a screw are created by various subtractive processes (including cutting [single-point, taps and dies]; molding; casting [die casting, sand casting]; grinding]; and occasionally additive techniques such as deburring. The threads are then grouped together in groups called thread sets and bonded with an adhesive such as epoxy or molten lead. Metric threads are sized by diameter and pitch, or the space between threads, with coarse threads being the industry standard. A screw with a diameter of 5 mm has a 1 mm pitch. 3/8 in to mm