Self-tapping screws are concrete screws that tap threads into the base material such as concrete, brick or block. A hole must first be drilled into the base material and, as the concrete screw is inserted into the hole, the threads are tapped. There are many brand names of concrete screws on the market today. The original self-tapping and the most widely recognized one is called Tapcon, which is derived from Tapping Concrete.
Other brand names and links are listed below:
The self-tapping concrete screw was developed by ITW Buildex in the late 1970’s and arrived in the marketplace during the early 1980’s being sold with the brand name of Tapcon. Tapping concrete with a screw is a very unique process and requires a number of specific guidelines in order to achieve holding values.
Diameters of Self-Tapping Screws
The two groups of self-tapping screws are organized by diameter. The first group is the standard self-tapping screw that is manufactured in the two diameters of 3/16” and 1/4”. The other group is the large diameter self-tapping screw that is available in diameters of 3/8”, 1/2”, 5/8” and 3/4”.
For the purposes of this article, only the standard self-tapping screw will be described. For more information on the large diameter self-tapping screw, go to /diy-articles/large-diameter-tapcons.
The 3/16” and 1/4” self-tapping screws are both manufactured in two different head styles. Each head style is designed for use in a specific type of application. The flat head Phillips countersunk self-tapping screw is used in applications in which the top of the head must sit flush with the surface of the material being fastened. This requires that the material being fastened has some thickness and that the hole is designed to fit a countersunk headed fastener. An example of this type of fastening would be a cabinet where the head of the screw would sit flush with the surface and would not protrude into the interior of the cabinet. The other head style is the hex head that is slotted and has a manufactured washer attached to the head. This hex slotted washer-headed self-tapping screw works for applications in which the head of the screw is above the surface of the material being fastened and a wider bearing surface is required. An example of this type of application would be a conduit strap into concrete.
Both diameters of self-tapping screws require a different size driver to be used for installation. The 3/16” hex head needs a 1/4” nut driver and the 1/4” hex head needs a 5/16” driver. The flat head 3/16” self-tapping screws use a #2 bit tip or screwdriver and the 1/4” uses a #3 bit tip.
The hole that must be drilled into the base material must be a specific size and matched to the diameter of the self-tapping screw being installed. To ensure that the hole size will match the diameter of the screw, always use a carbide tipped bit that meets ANSI standards. The diameter of the hole that needs to be drilled for a 3/16” diameter is 5/32” and the diameter of the hole for the 1/4” diameter is 3/16”.
When drilling a hole for a self-tapping screw, the hole must be drilled a minimum of 1/4” deeper than the screw will penetrate the base material. This extra space will ensure that the screw will not bottom out in the hole after the dust created from the tapping process is deposited at the bottom of the hole.
Length of Screw
The hex head self-tapping screw is measured from under the head to reflect the length of the screw that will penetrate both the material being fastened and the base material. The flat head self-tapping screw is measured to include the head because the whole length of the screw will penetrate the material being fastened and the base material.
Minimum/Maximum Length of Screw
To determine the minimum length of self-tapping screw to use, add the thickness of the material to be fastened to the minimum embedment of 1”. Adding the thickness of the material being fastened to the maximum embedment of 1-3/4” will calculate the maximum length of screw to use.
Installing Self-Tapping Screws
- Drill hole using a hammer drill in the hammer mode, with the correct diameter carbide tipped bit that meets ANSI standards.
- Drill the hole to a depth of at least 1/4” deeper than the self-tapping screw will penetrate the base material.
- Clean the hole of all dust.
- Insert self-tapping screw through the material being fastened and into a hole in the base material.
- Turn the self-tapping screw clockwise with a screwdriver, drill set in the rotation mode or wrench until the head of the self-tapping screw is tight against the surface of the material being fastened.