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Oak

Oak Series 400

Very little is known about Oak’s non-membrane keyboard switches.

Oak advertised (in 1973) a type of tall, transparent, mechanical switch as Series 400. The current owner of Oak Industries’ switch line reports that no details remain on the keyboard switches.

A switch matching this visual depiction showed up in a Honeywell 80-02 keyboard, from a Honeywell 5921 terminal.

There are also tall switches in some unidentified Facit keyboard that appear to be Oak, but the bases of them are opaque instead of transparent.

Oak Series 400 is named in US patent 3924722 (but not in Google’s transcript at the time of writing, which is erroneous — download the PDF), an electronic typewriter patent from CPT Corp, filed in 1973, the same year as the advertisement.