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Alps switch model numbers

Alps keyboard switch model numbers take the form SKxyza, where the positions have the following interepretations:

x
Thus far, this seems to indicate contact classification, with “C” covering switches with switchplates (SKCC, SKCL/SKCM and SKCP), “E” covering integrated domes (e.g. SKEW), and “F” covering bare metal contacts (including non-“switchplate” contact modules; thus far, SKFL, SKFM/SKFN and SKFR/SKFS)
y
Series indicator within the above classification, such as “B”, “C”, “L”, “M” and “P” within SKCy; these are often paired, with the linear type having the lower of two adjacent letters (SKCL/SKCM, SKFM/SKFN, and SKFR/SKFS)
z
Subseries, covering a particular set of characteristics (see below)
a
Individual switch model letter; this last character remains a complete mystery. In some subseries, it starts at “A” (such as SKFSAA or SKFNAA) while with other subseries the earliest character is at least a few letters in (as with SKFRAC, the lowest known SKFR model, and SKCLJC, the lowest SKCLJa type, and it’s never clear whether all subtypes started at A or whether some subseries skipped the first few letters).

“SK” is reported to stand for “single key switch” according to Sandy, per the 1994 catalogue. This may not be a literal meaning, but rather it might be a convenient interpretation for English-speaking customers.

Series names

The exact format of Alps series names remains a mystery, because so little documentation has been located. There is good evidence that SKCL and SKCM were called “CL series” and “CM series” (both in the 1994 catalogue and in the late 80s), but information that seemingly arrived via Sandy indicates that in the 1994 catalogue, CM and CL series were found alongside SKFR and SKFS series. Further, “SKCL/SKCMシリーズ” (“SKCL/SKCM series”) has been used in an official Alps document. Further, Apple technical literature also gives “KCC” for SKCC and “KFF” for SKFF along with, confusingly, “KBB” for SKCC. Unforunately, unlike with the Datanetics keyboards, no Alps switch part numbers are cited.

Subseries

Series are divided up into subseries based on switch type. It seems that some subseries letters (in particular F) are shared between more than one series.

Subseries Example meanings
A In all examples to date, “A” covers single-pole, single-throw normally-open momentary switches. In SKCC series, it appears to indicate switches with a tall slider.
B In SKCM series, it appears to denote damped (SKCMBB: SKCM Cream Damped), while in SKCC series, it appears to denote standard slider height.
C The only known example is SKCMCQ, which seems to be a replacement model number for white Alps (SKCMAQ); it seemed like “C” might denote bamboo switches, but as SKCM Green model SKCMAT seems to be bamboo, the meaning of “C” and the difference between SKCMCQ and SKCMAQ remains a mystery.
F In all examples to date, this indicates an illuminated switch. This is SKCLFQ (SKCL Yellow with red LED) and SKCLFM (SKCL Yellow with green LED) from SKCL series, and SKFRFA (red LED), SKFRFB (green LED) and SKFRFC (amber LED) from SKFR series.
J Alternate action (SKCLJC: grey Alps Lock)
K Double action (SKCLKB)