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Keyboard glossary

1A
Single Pole Single Throw Normally Open
1B
Single Pole Single Throw Normally Closed
2A
Double Pole Single Throw Normally Open
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
DPDT
Double Pole Double Throw
DPST
Double Pole Single Throw
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
Full travel
Not clearly defined; see under travel
Hysteresis
After actuation, the switch must be released a short distance to release; see under travel
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
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”
Slider
A community term for plunger; its origins are probably just as lost as those of “switchplate”, and sadly 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
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 angle is 0° (vertical)
Travel
The vertical motion of the switch; see under travel