Keycap mount

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Template icon--Diagram.svg This article requires illustration in the form of diagrams — Would be nice to have diagrams of each mount with dimensions

A keycap mount is the interface between a keycap and a switch. Some mount types are standardized between switch and keycap manufacturers.

Integrated mounts

A mount is "integrated" when the bottom part of the keycap is the switch mechanism's primary slider. Integrated mount is not a standard: integrated mount keyboards are not incompatible with each other.

Snap-on mounts

Snap-on mounts have flat-topped sliders onto which the keycap is affixed. Snap-on mounts are all proprietary and are not compatible between keyboard types.

Examples:

Cherry MX mount

Cherry MX switch and its mount

A cross-shaped stem on the switch's slider into a cross-shaped hole within a cylindrical stem in the bottom of the keycap. This is often called a "Cherry MX mount" because it is found on Cherry MX switches. Whether the mount type has an industry-wide designation is unknown.

Cherry's MX keycap specifications give the keycap slot dimensions as a cross 4.1+0.05 mm wide, with arms 1.17±0.02 mm wide[1] (this would make them 1.465 mm long). There are no known specifications for the switch stem.

Signature Plastics gives the dimensions (presumably of the keycap) as a cross 0.159ʺ (4.04 mm) wide, with arms 0.047ʺ (1.19 mm) wide.

Cherry M8 switches use a cruciform mount with the same lateral dimensions as MX switches, but with a shorter switch stem. This shorter stem leads to keycap incompatibility. Cherry produced a Cherry MX-M8 Adapter variant of the Cherry MX switch family which allowed the use of shorter M8 keycaps on otherwise standard MX switches.

See: keyboard switches with Cherry MX mount

Switches

... and more

Keycap manufacturers and vendors

Additional keycaps are made/sold by:

... and more

Notes

There are also some mount types that are quite similar but not exact like the Cherry MX mount. There are switches with a cylinder around the stem, and there are keys with struts in-between the keycap stem and keycap wall that make it not "Cherry compatible" without modification.

Hirose Cherry mount

Hirose Cherry mount is a smaller cross than Cherry MX mount. Cherry MX keycaps will fit on Hirose Cherry switches, but Hirose Cherry keycaps will not fit on Cherry MX mount keycaps. The horizontal arms are shorter but approximately the same thickness, but the vertical arms of the cross are noticeably thinner, and keycaps made for this mount won't fit onto a Cherry MX mount keycap.

Custom cruciform

There are many keycap mounts that look very similar to Cherry MX mount, but have incompatible dimensions. They will not take Cherry MX keycaps. Such mounts include those of Cherry M6 and Cherry M7 switches. The slider dimensions are not always 90° rotationally symmetrical: one pair of cross arms may be thicker than the perpendicular pair of arms.

Tee and bar mount

Numerous switch types have tee (⊢) and bar (|) mount sliders. Such switches typically take cross-mount keycaps, and as such, the switches support full 90° rotational symmetry. For example, the Alps SKCC series switch has been found mounted in several orientations, without affecting keycap fit.

Alps mount

Alps-mount keycap and Alps SKBM White switch

A type of mount that is very common for different types of switches. The slider has a slot that is around 4.6 mm × 2.3 mm at the top; the keycap has rectangular peg around 4.5 × 2.2 mm. It is used on various Alps switches including the Alps SKCL/SKCM series, and is therefore most often called "Alps mount". The term "Alps mount" does not mean that all Alps switches used this mount: some switches use similar but incompatible mounts, and many more use use totally different mounts. There are more switch types from third parties that use this mount than there are in Alps Electric's entire product range.

Whether there is an industry-wide designation for this type of keycap mount is unknown.

Switches

See keyboard switches with Alps mount. Most notable switches:

Keyboards

See keyboards with Alps switches for keyboards with the Alps and Alps clone switches.

Rubber dome keyboards:

  • Monterey K208 (rubber dome keyboard)
  • Smartboard rubber dome keyboards

Keycap manufacturers and vendors

Additional keycaps can be purchased from:


RAFI mount

The slider has a cubical top with an edge length of 5 mm, underneath of wich are two tiny lugs on opposite sites. The keycap has a mating square hole and recesses where the lugs engage when the keycap is snapped on the slider. RAFI described the mechanism in a patent from 1975, GB 1533154 , but did not put any claims on it.

Switches

Notes

First known uses where by RAFI (1975), Siemens (1980) and Sasse (1981); intermarriage is possible at laeast for some pairings (Siemens on RAFI and vice versa, Siemens on Sasse).


Mitsumi mount

Mitsumi mount keycap and tactile Mitsumi hybrid switch

Used for Mitsumi hybrid switches and Mitsumi mechanical switches. Square peg (keycap) inside a square hole (slider).


Key Tronic mount

Sliders are cylindrical and hollow with a bar inside. Each keycap has two fingers that snap onto the bar.

Most often these are Key Tronic foam and foil switches with a rubber sleeve or coiled spring around the slider, but the mount type is also found in keyboards from Alphameric with different switches.[2]


Topre mount

Clare-Pendar mount

This is a cruciform mount. General Instrument Series S950 differs from Alps SKCC Series by its use of Clare-Pendar mount keystems. This mount should also cover other Clare-Pendar switch types.

Marquardt mount

Used on Marquardt's electric typewriter switches. The mount provides two plastic prongs, each approximately 1 mm × 2.5 mm in cross section and around 4.9 mm tall, with a 1 mm gap between them.

References

  1. File:Cherry MX 1×1 keycap specification (1983).pdf
  2. Deskthority thread Telex Keyboard?. Posted 2014-04-05.