![Schroef](https://upload.wikimedia.org/wikipedia/commons/c/cc/Schroef.jpg)
A self-tapping screw is a
screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
that can
tap its own hole as it is driven into the material. More narrowly, self-tapping is used only to describe a specific type of thread-cutting screw intended to produce a thread in relatively soft material or sheet materials, excluding
wood screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
s. Other specific types of self-tapping screw include self-drilling screws and thread rolling screws.
Mechanism
![Vis-auto-taraudeuse](https://upload.wikimedia.org/wikipedia/commons/5/5a/Vis-auto-taraudeuse.jpeg)
Self-tapping screws have a wide range of tip and thread patterns, and are available with almost any possible
screw head
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
design. Common features are the screw thread covering the whole length of the screw from tip to head and a pronounced thread hard enough for the intended
substrate, often
case-hardened
Case-hardening or surface hardening is the process of hardening the surface of a metal object while allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal at the surface. For iron or steel with low carbon ...
.
For hard substrates such as metal or hard plastics, the self-tapping ability is often created by cutting a gap in the continuity of the thread on the screw, generating a
flute
The flute is a family of classical music instrument in the woodwind group. Like all woodwinds, flutes are aerophones, meaning they make sound by vibrating a column of air. However, unlike woodwind instruments with reeds, a flute is a reedless ...
and cutting edge similar to those on a
tap. Thus, whereas a regular
machine screw
A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to fa ...
cannot tap its own hole in a metal substrate, a self-tapping one can (within reasonable limits of substrate
hardness
In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
and depth).
For softer substrates such as wood or soft plastics, the self-tapping ability can come simply from a tip that tapers to a gimlet point (in which no flute is needed). Like the tip of a
nail
Nail or Nails may refer to:
In biology
* Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal digit, such as fingernail
* Nail (beak), a plate of hard horny tissue at the tip ...
or
gimlet, such a point forms the hole by displacement of the surrounding material rather than any
chip Chromatin immunoprecipitation (ChIP) is a type of immunoprecipitation experimental technique used to investigate the interaction between proteins and DNA in the cell. It aims to determine whether specific proteins are associated with specific genomi ...
-forming drilling/cutting/evacuating action.
Not all self-tapping screws have a sharp tip. The ''type B'' tip is blunt and intended for use with a
pilot hole
In construction, a pilot hole is a small hole drilled into a piece of construction material. Its purpose may be:
#to guide a larger drill to the appropriate location and ease the job of the larger drill
#allow for the insertion of another hole-m ...
, often in sheet materials. The lack of a sharp tip is helpful for packaging and handling and in some applications may be helpful for reducing the clearance necessary on the reverse of a fastened panel or for making more thread available on a given length screw.
Thread-forming vs. thread-cutting
Self-tapping screws can be divided into two classes;
those that ''displace'' material (especially plastic and thin metal sheets) without removing it are termed thread-forming self-tapping screws; self-tappers with sharp cutting surfaces that ''remove'' the material as they are inserted are termed thread-cutting.
Thread-forming screws may have a non-circular plan view, such as the five-fold symmetry of the
pentalobular or three-fold symmetry for Taptite screws.
Thread-cutting screws may have one or more flutes machined into their threads, giving cutting edges.
Self-drilling screws
![SelfDrillingScrewsx4](https://upload.wikimedia.org/wikipedia/commons/0/07/SelfDrillingScrewsx4.png)
Some self-tapping screws are also self-drilling, which means that, in addition to the tap-like flute in the leading threads, there is also a preliminary drill-like fluted tip that looks much like the tip of a
center drill
Drill bits are cutting tools used in a drill to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order ...
. These screws combine a
threading-like action and the fastener installation itself into only one driving motion (instead of separate drilling, tapping, and installing motions); they are thus very efficient in a variety of hard-substrate applications, from
assembly line
An assembly line is a manufacturing process (often called a ''progressive assembly'') in which parts (usually interchangeable parts) are added as the semi-finished assembly moves from workstation to workstation where the parts are added in seq ...
s to
roofing.
Brands such as the Tek screw integrate a self-drilling screw and sealing washer to quickly stitch together, for example, roofing sheets.
Sheet metal screw
Sheet metal screws (sometimes called "sheet-metal self-tappers", or P-K screws from the brand name ''Parker Kalon'' - who pioneered
the manufacture of, but did not invent, these screws) are a type of self-tapping screw despite the thread created in the sheet of metal being small.
Pan-head PK Self-tapping screws are common in electrical equipment, while flatter-headed truss or flat countersunk headed self-tapping screws
are more common in aviation applications.
Winged self-tapper
Winged self-drilling have thin wings wider than the thread formed just behind the self drilling head. These cut a clearance hole in soft materials (such as wood or plastic), but are destroyed by more robust materials (such as metal). Thus, to clamp some material to metal, the clearance drilling, tap drilling, thread tapping, and fixing itself can happen in a single operation from one side, with the materials in their final position.
Applications
Self-tapping screws are used in a variety of applications ranging from
DIY
"Do it yourself" ("DIY") is the method of building, modifying, or repairing things by oneself without the direct aid of professionals or certified experts. Academic research has described DIY as behaviors where "individuals use raw and semi ...
carpentry to
surgery
Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...
.
Surgical
Dental implant
A dental implant (also known as an endosseous implant or fixture) is a prosthesis that interfaces with the bone of the jaw or skull to support a dental prosthesis such as a crown, bridge, denture, or facial prosthesis or to act as an orthodonti ...
s and
orthopedic bone screws are both examples of self-tapping screws used in surgery. Different thread profiles are used for either denser
cortical bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
or the spongy
cancellous bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and ...
.
See also
*
Fasteners with a tapered shank
*
Tap
References
External links
"Hold Everything", February 1946, ''Popular Science''bottom of page 151
{{DEFAULTSORT:Self-Tapping Screw
Screws