Gender of connectors and fasteners

thumb|Schematic symbols for male and female connector pins

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This article describes a technical nomenclature standard for many existing engineered systems. The traditional "male/female" and "gender" designations are still widely used in technical communications, without cultural or political intent. Do NOT make unreferenced changes to the nomenclature in this article without first discussing them with other editors on the Talkpage. Unilateral changes to terminology which lack relevant citations will be reverted to their previous state.

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In electrical and mechanical trades and manufacturing, each half of a pair of mating connectors or fasteners is conventionally designated as male or female, a distinction referred to as its gender. The female connector is generally a receptacle that receives and holds the male connector. Alternative terms such as plug and socket or jack are sometimes used, particularly for electrical connectors.

The assignment is a direct analogy with male and female genitalia. The part bearing one or more protrusions, or which fits inside the other, is designated male, while the one with the corresponding indentations, or fitting outside the other, is designated female. Extension of the analogy results in the verb to mate being used to describe the process of connecting two corresponding parts together.

In some cases (notably electrical power connectors), the gender of connectors is selected according to rigid rules which enforce a sense of one-way directionality (e.g. a flow of power from one device to another). This is done to enhance safety, or ensure proper functionality, by preventing unsafe or non-functional configurations from being set up.

In terms of mathematical graph theory, an electrical power distribution network made up of plugs and sockets is a directed tree, with the directionality arrows corresponding to the female-to-male transfer of electrical power through each mated connection. This is an example where male and female connectors have been deliberately designed and assigned to physically enforce a safe network topology.

In other contexts, such as plumbing, one-way flow is not enforced through connector gender assignment. Flows through piping networks can be bidirectional, as in underground water distribution networks which have designed-in redundancy. In plumbing situations where one-way flow is desired, it is implemented through other means (e.g. air gaps or one-way check valves), and not through male-female gender schemes.

Early mentions of the metaphor

thumb|[[An Universal Etymological English Dictionary|Universal Etymological English Dictionary mentioning male and female screws in 1731]]

The Talmud describes arrow heads and mating shafts as potentially being either male or female, depending on their construction, i.e. a prong on a male arrow head fits into a hollowed out shaft and vice versa. This is owing to a prohibition on a female shaft, from its susceptibility as a receptacle for impurity, for use as s'chach.

18th-century dictionaries and encyclopedias mention male and female screws or cochleae. A 1736 builder's manual mentions screw genders as metaphors for convex and concave shapes:

Mechanical fasteners

thumb|left|Female nut threaded onto a male bolt

In mechanical design, the prototypical male component is a threaded bolt, but an alignment post, a mounting boss, or a sheet metal tab connector can also be considered as male. Correspondingly, a threaded nut, an alignment hole, a mounting recess, or sheet metal slot connector is considered to be female.

While some mechanical designs are one-time custom setups not intended to be repeated, there is an entire fastener industry devoted to manufacturing mass-produced or semi-custom components. To avoid unnecessary confusion, conventional definitions of fastener gender have been defined and agreed upon.

Modular construction toys

thumb|Lego toy brick connections are female underneath, and male on top

Several common construction toys embody gendered (and in some cases, genderless) mechanical interconnections. For example, the canonical Lego plastic blocks have female indentations on the lower surface and male bosses, or protrusions, on the upper surfaces. Meccano and Erector have many gendered connections, starting with the nut-and-bolt fasteners they use frequently.

Stickle bricks, using interlocking plastic protrusions, are effectively genderless (while nonetheless maintaining an asymmetry). Lincoln logs use a very simple form of genderless connections. Kapla or KEVA planks are extremely simple genderless systems interconnected only by gravity.

Mathematicians have begun to classify well-known construction sets using group theory to study the combinatoric possibilities of structures that can be built.

Plumbing

thumb|left|Left: A male threaded pipe,<br />Right: a female threaded [[Piping and plumbing fittings|elbow]]

In plumbing fittings, the M or F usually comes at the beginning rather than the end of the abbreviated designation. For example:

MIPT denotes male iron pipe thread;
FIPT denotes female iron pipe thread.

A short length of pipe having an MIP thread at both ends is sometimes called a nipple. A short pipe fitting having an FIP thread at both ends is sometimes called a coupling.

Hermaphroditic connections, which may include both male and female elements in a single unit, are used for some specialized tubing fittings, such as Storz fire hose connectors. A picture of such fittings appears in , below. Interchangeable garden hose fittings made by GEKA are also hermaphroditic, relying on a rubber gasket to make the final connection.

Downspout

Downspouts (also called downpipes, rain conductors, or leaders) are used to convey rainwater from roof gutters to the ground through hollow pipes or tubes. These tubes usually come in sections, joined by inserting the male end (often crimped with a special tool to slightly reduce its size) into the female end of the next section. These connections are usually not sealed or caulked, instead relying on gravity to move the rainwater from the male end and into the receiving female connection located directly below.

Ductwork

Sheet metal ductwork for conveying air in HVAC systems typically uses gendered connections. Typically, the airflow through a ductwork connection is from male to female. However, connections formed opposite to this convention can be seen in some systems, since all connections are typically sealed with duct sealing mastic or tape to prevent leakage anyway. The flow convention is usually loosely adhered to for simplicity of design and to reduce the number of gender changer fittings required, but exceptions are made whenever expedient.

Electrical and electronic

Although the gender of tubing and plumbing fittings is usually obvious, this may not be true of electrical connectors because of their more complex and varying constructions. Instead, connector gender is conventionalized and thus can be somewhat obscure to the uninitiated. For example, the female D-subminiature connector body projects outward from the mounting plane of the chassis, and this protrusion could be erroneously construed as male. Instead, the gender is determined by the innermost part, the male pins, rather than by the protrusion of the connector that fits inside the shield of the mating connector. (This is also true for many other pin-based connectors, like XLR). The distinction is more obvious with ring crimp lug connectors which are placed around a screw post, but again with spade or split ring crimp lug connectors the end alone is not obviously female.

Further confusion can be caused by the term jack, which is used for both female and male connectors and typically refers to the fixed (panel) side of a connector pair. IEEE STD 100, IEEE-315-1975 and IEEE 200-1975 (replaced by ASME Y14.44-2008) define plug and jack by location or mobility, rather than gender.

A connector in a fixed location is a jack, and a moveable connector is a plug. Cost and reliability considerations probably drove the design decision to use female jack connectors on many computer terminals (and some personal computers) for the serial port, despite being in direct violation of the connector gender convention explicitly specified in the RS-232 standard for DTE (data terminal equipment) connections. This confusing reversal of the RS-232 connector gender convention has caused many hours of frustration for ill-informed end users, as they tried to troubleshoot non-functional serial port equipment connections.

Safety

thumb|upright|Electrical power outlets are female for safety.

In electrical connections where voltage or current is sufficient to cause injury, the part permanently connected to the power source is invariably female, with concealed contacts, to prevent inadvertent touching of live conductors by people or animals, or by conductive items that may cause a short circuit. A male plug, with fully exposed protruding contacts, is installed on the cord of (or directly onto) the device receiving the power. Devices that need to be robust against mechanical damage may use a special male IEC 60320 C14 connector (see the gallery above), which is recessed below the surface of a mounting panel, providing the desired physical protection while conforming to safety regulations.

In the case of consumer-level AC power, connector gender is used to implicitly enforce safe use of power connectors. Because of this consideration, it is illegal under electrical code to make or use any gender changers to connect AC line power to consumer-level equipment.

thumb|A dangerous double-ended male connector, known as a "suicide cable"

A double-ended male connector for utility-supplied (mains) electrical power is extremely dangerous, and sometimes is called a "suicide cable" or "widowmaker cord". Some hardware shops explicitly refuse to make or sell them when asked by customers who have mistakenly hung a string of Christmas lights backwards and wish to connect the socket end to a wall socket, or who intend to connect a generator or inverter to their home's electrical circuit in the event of a utility power outage. Another style of connector uses hybrid male/female pins with a receiving slot fitted in the center of each two-tine pin, and relies on 90-degree rotation of the pin axes to mate. The connector housings themselves are sexed male and female.

Gender changers

Devices used for mating two connectors of the same gender and referred to by a wide variety of terms, including, for example: gender changer, gender mender, gender bender, and gender blender. A specific gender changer can be referred to by either the gender of its connectors, or the gender which it is designed to connect to, resulting in a thoroughly ambiguous terminology. Thus a male gender changer might have female connectors to mate two male ends, or male connectors to mate two female ends.

Adding to this potential for confusion, some gender changers also combine additional functions such as cross-over conductor assignments. Active cables may incorporate embedded systems for communications protocol or logic level changes, which technically makes them adapters, but this distinction is sometimes neglected in marketing materials or common usage.

Examples

Coaxial power connector, for low-voltage DC connections
A power cord on an appliance terminates in a (male) plug; it connects to a (female) socket in a wall or on an extension cord.
Coaxial cables used for video or other high-frequency signals are normally terminated, at both ends, in a connector comprising an inner pin and an outer fixed or rotating shell; these are conventionally reckoned as male.
A threaded nut is female and a bolt is male.
Connectors for air brake hoses on heavy trucks and railroad equipment use genderless gladhand connectors. In railroad air brake use, this makes the orientation of rolling stock irrelevant, and is used with the standard North American railroad coupler that connects cars together, also genderless.