Cherry M1 (or M11, depending on how you interpret the M11-0101 drawing) is a customer-specific series created for HP as a drop-in replacement for Datanetics DC-60 series, with the dimensions matching those of DC-61-06. The most telling characteristic is that, unlike all other contemporary hard contact Cherry switches, M1 is single-pole only, with the internal arrangement adjusted to move the terminals to the centreline. In effect, M1 is an M9 switch rearranged to match the dimensions and keystem of DC-60.
DC-60 itself was introduced in 1973, primarily for Monroe, as a low-cost switch for high-end calculators. The M11-0101 drawing itself is dated November 1979, placing it well after DC-60 was introduced. M1 is however based on the tallest type (DC-61-05/DC-61-06), whose introduction seems to be between 1975 and 1981.
M1 is only known from HP keyboards, and has two discovered variants:
- Black: regular
- Clear (M11-0101): 95±25 cN: space bar (per the drawing), with customer part or request number 3101-0469
The presence of a customer part/request number on drawing is another indication that this was a customer-specific part.
Credit for making the connection goes to Findecanor in a forum post made in 2014, almost two years prior to the identification of DC-60 series.
UncleFan sent me this photo from Brother Dragon (yab8433408) showing an HP keyboard with what appear to be the MX-mount DC-60 switches, alongside an M11-0101 for space:
Confusingly, these cream switches are (in the examples previously found for sale separately) the medium profile type, which makes them distinctly shorter than M11. At present, nothing more is known about the keyboard shown above.
The question of M1 or M11 remains unanswered. The part numbers do not follow the common schema. The part numbers follow the old system used with M41–M78, and being a German switch this would suggest M1, initial subtype, single pole. Being a custom series, Cherry Mikroschalter may have started allocating these up from M1. If this is true, it re-opens the possibility that MX really does denote series 10, with the Roman numeral X for 10. While it is true that a present-day unnamed German employee is noted for seeing a resemblance between these switches and “M10”, no explanation for “M10” has ever been found.