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Keyboard glossary

Contents

General list of terms

1A
Alternative term for Single Pole Single Throw Normally Open (SPST-NO)
1B
Alternative term for Single Pole Single Throw Normally Closed (SPST-NC)
2A
Alternative term for Double Pole Single Throw Normally Open (DPST-NO)
A/W
(On PCBs from Alps USA and Hi-Tek) Artwork (confirmed from a keyboard where it was written out in full)
Alternate action
The switch alternates between open and closed each time it is pressed. Typically, the plunger will sit lower when the switch is closed, and will return to its original position when released, but Clare-Pendar for one differentiate between alternate action (which simply changes state) and latching (where the plunger is held in a lower position when the switch is closed). Other terms for such switches are locking and push-push.
Bar mount
See under straight mount
Diaphragm
See under membrane, below
DPDT
Double Pole Double Throw
DPST
Double Pole Single Throw
Flexible printed circuit
A printed circuit that uses a flexible sheet of plastic (generally polyester) instead of a rigid board, which can be found in membrane keyboards; the circuit tracks are generally described as being a silver–carbon ink
Form A
Single Pole Single Throw Normally Open (also written 1A, especially by Cherry) or simply Normally Open
Form B
Single Pole Single Throw Normally Closed (also written 1B, especially by Cherry) or simply Normally Closed
FPC
See under flexible printed circuit, above
Full travel
Not clearly defined; see under travel
Hysteresis
After actuation, the switch must be released a short distance to release; see under travel
Keycap
See under plunger below
Keytop
Another term for keycap
Keystem
See under plunger below; on this site, “keystem” is used to mean the vertical post on the plunger that holds the keycap via a friction fit
Latching
See under alternate action, above
Mechanical
Metal contacts, operated through physical engagement (rather than by a magnet, as in reed switches); see switch types
Membrane
A thin, flexible layer of material; in membrane keyboards this refers to the layers of plastic (typically Mylar polyester) used for the flexible printed circuits and the intermediate spacer layer (Datanetics used the term “diaphragm” for their flexible printed circuits, and in DC-50 switches, for the outer layers of plastic)
Momentary
The switch is only closed when the plunger is held down; once you let go, the switch opens again.
N-key rollover
The ability to detect an unlimited number of simultaneous keypresses; currently known from as early as 1979 (US patent 4278965)
NC
Normally Closed
NO
Normally Open
Overtravel
Further travel after actuation; see under travel
Pre-travel
The distance a switch can be pressed up to the point that it actuates; see under travel
Push-push
See under alternate action, above
PWB
(On PCBs from Alps USA and Hi-Tek) Likely “Printed Wiring Board”, an alternative term for printed circuit board (PCB)
Slider
An alternative term for plunger; this term would have been better applied to switches with internal horizontal sliding components (in particular Sasse Series 25 and Alps SKFL Lock)
Solid state
Non-contact switching (e.g. Hall effect, magnetic valve, foam and foil); see switch types
SPDT
Single Pole Double Throw
SPST
Single Pole Single Throw
Stem
Possibly short for “keystem”; see under plunger below.
Straight mount
A thin, oblong keystem; this has also been referred to as “bar mount”, which helps differentiate between “straight” being used to indicate that the keystem vertical angle is 0° (upright)
Travel
The vertical motion of the switch; see under travel

Details

Plunger

The component of a pushbutton switch that provides the vertical motion is most commonly termed the “plunger”. The part of the key that you see—with the inscription that tells you what the key does, such as “Q” or “Shift”—is called the “keycap” or “keytop” (or sometimes translated as switch hat). The keycap is generally a separate part that attaches onto the plunger of the switch. The keycap is normally a press fit (friction fit), into a slot or onto a post on the plunger, but it may also clip on.

The plunger may also be called a “keystem” (including in historical patents), and particularly with Cherry MX switches this is shortened to simply “stem”. This is confusing, as “stem” implies a narrow object; it may be that the post that holds the keycap has become a metonym for the entire plunger.

Another widely-used term in keyboard enthusiast community is “slider”. This is rarely seen in official literature, but the cross-section diagram in the datasheet for Fujitsu FKB4690 Series spring-over-membrane keyboards refers to the plunger as “スライダー”: “slider” (phonetically, “suraidā”). “Slider” could be a Japanese term, which may explain why Alps SKCL/SKCM plungers are most commonly associated with the term “slider”, while German Cherry switches have “stems”. US patent 4529849 from Fujitsu (filed in 1983) uses “slider” in English, while US patent 4642433 for Alps SKCM uses “stem”.

Within this site, the moving part is referred to as a “plunger” to best accommodate standard English-language terminology, although older pages will still say “slider”. The term “keystem” is adopted here to refer specifically to the projection on the plunger that holds the keycap. Where the plunger is slot-mount, the keycap has the stem instead.