Cherry M5, M6 and M73/M74 design
- Keycap mounts
- Plunger colours
- Upper shell
The external shape of a Cherry M5, M6, M73 and M74 switch indicates broadly which series the switch comes from (M5 or M6 series made in the US or Japan, or M7 series made in Germany), and with US switches, an indication of its generation. The internal details also differ between switches made in Germany, and those made in the US and Japan. These differences are detailed below.
In the 1973 and 1974 US catalogues, the only keycap mount offered was “straight” (a flat or “blade” stem), unofficially described as “bar” (because “straight” implies 0° angle rather than flat shape). By 1979—the next US catalogue discovered—T stem had become an option, although the majority of switch types listed for sale remained straight mount. Discovered M5, M6 and M7 examples from the early-to-mid 1970s are extremely rare, so it is not clear when T stem became available. German switches supported T stem as early as 1976, as shown in the drawing for M73-0110, which is straight stem but it shows the Style C design with full support for T and cruciform stems. All standard keystems accept Cherry’s 12 mm keycaps.
After T stem became the de facto mount, space bar switches (in the US, at least) could still be found with a straight stem, such as in the Contact Systems CS-400CD (B70-4753). This was significant because some space bars were moulded to only accept a straight stem, unlike all other keycaps that used a cruciform slot that would accept T stem switches or any orientation of straight stem switch.
Alternate action and double pole also remained straight stem in the US, simply because the design of the switch did not permit a T stem to be combined with the alternate action mechanism or a second pair of contacts. The German design did not suffer from this limitation.
In US convention, T-stem switches typically face right (⊢) with terminals 1 and 2 on the left, or in some cases forwards (⊥) with those terminals at the front. There does not seem to be any consensus for switch orientation with German-designed keyboards.
The majority of plungers are black. Where colour coding was used, it was not universal or consistent. Known uses of colour include:
- Alternate action: grey
- German-made M51-0131: grey
- US-made 10° stem: often white (pigmented)
- Style D switches in SAGEM keyboards can also be blue or white according to function
The Blaupunkt CEPT-Btx-C1 keyboard has M7 switches with clear stems, and these switches are tactile (described as being akin to MX Brown). Space bar is a straight stem, just as with US-made keyboards (and this has a black stem and a hint of red paint), while the remainder of the keys are T stem. The clear stem tactile switches lack the 1-2-3-4 numbers moulded into the top. From the few photos that UncleFan managed to obtain from the owner (Spharx) it seems that some switches may also be double pole, but sadly this extremely rare example was terribly poorly documented, as is so often the case, and no more information has been forthcoming.
The standard momentary and alternate action switches from Cherry gold crosspoint (latterly M4/M5/M6 Series) and Serie M7 are broadly divided into approximately five different styles. This classification was created around 2016 before these switches were better understood, and the significance of these styles is still a matter of ongoing research; see the M4/M5/M6 examples and M7 examples pages for further information. Some styles have visually significant variation that may have chronological or other significance; these are classified as sub-styles.
Styles A, AB and B are the US-made switches, in apparent production order (AB was overlooked from the original classification and appears to fall between A and B, sharing characteristics of each). Switches from these styles fall within M5 and M6 Series. Style C represents the German-made switches in Serie M7, specifically the basic design (single or double pole, non-illuminated) covered by M73 and M74. Style D is also M7, and is a custom type made for SAGEM. M5 and M6 switches were also manufactured by Hirose Cherry Precision in Japan; Style B′ is known to have been made in Japan, but currently there is no evidence to indicate whether Style B′ was made in the US or Style B in Japan.
The US-made switches are all smooth finish. The German-made switches appear to have started with smooth sides and a textured top, changing to all-over textured finish (seemingly the same as with M9), although this remains speculation due to the rarity of German M7 keyboards. Style D switches appear to all be textured finish.
The style classification only covers the standard momentary and alternate action switches. M4 (corner illuminated) and M71 (centre illuminated) and most designs from M75–M78 (triple and quad pole, dual illuminated, and double-pole alternate action) are all distinct designs that can be recognised directly. M76-0899 uses a Style C shell with a custom keycap mount. This DPDT alternate action model is an example of an M76 switch with no illumination, but being DPDT the use of paired half-width contacts is externally evident from the terminal layout, allowing it to be identified as M76 without requiring the switch to be opened.
The styles are illustrated below. The differentiating characteristics of each style are highlighted in green for the purposes of recognition and identification. The drawings are broadly accurate to 0.1 mm, access to parts permitting. Some of the drawings were made possible or able to be significantly more detailed by way of additional photographs and parts supplied by Cherry collector UncleFan. Note that there was quite a bit of production variation, and the drawings below will differ from some switches.
Style A is the original design. Momentary switches have two tall posts on the top. The purpose of these posts is uncertain; the catalogues suggest that they are for mounting an illumination kit. After M4 and M71 series illuminated switches were introduced, these mounting kits became redundant, as would the posts if this was their purpose. Even so, at least one circle is present on the top of almost all later switches, typically raised, but recessed in the case of Style B. Style D is the only style where they are completely removed. In Style AB, one of these vestigial posts is typically used for a mould identifier.
An original mechanical keyswitch sample pack featuring 261-0100 (single pole momentary, later M61-0100), 262-0100 (double pole momentary, later M62-0100) and 261-0800 (single pole alternate action, later M61-0800) does not use these posts on the alternate action switch. This may be because Cherry felt that customers would not expect an alternate action switch to have illuminated status, since the latching state already gives a physical and visual indication. Nonetheless, M4 switches did become available in illuminated alternate action form.
In rare cases, momentary Style A switches have the side posts reduced to small nubs. These are classified as Style A′. Technically Style A′ only covers momentary switches, as the side posts were never knowingly used on alternate action switches (although it is certainly possible that custom models were made as such). Classifying the alternate action switches as Style A′ (according to their form) would give the incorrection impression that Style A′ appeared earlier than it did, but calling them Style A (by production era) would also be confusing as it would appear to be a classification error, as the “style” notion is only a fabricated concept of visual form and not of production history.
Style AB falls in between A and B, with the offset wall around the plunger aperture of B, but the squeeze-grip retention ramps of Style A. The posts are, as with A′, reduced to small stumps. The front post position (where the mould number is placed) can be either a recessed slot or a raised post (which raises more questions about the purpose of these circular positions). Tentative evidence places Style AB around 1979–80, making it a very short-lived and uncommon revision of the design.
Style B is notable for introducing distinct plate retention prongs. There is only one vestigial post position, offset from the centre, which appears to always be recessed. Style B is seen—albeit inaccurately drawn—in the Cherry M51-0131 design drawing. Based on ambiguous annotations to the drawing (those marked K1) there is a tentative suggestion that this switch changed to Style B in 1979, which would give the approximate age of this style. In examined keyboards, Style B first appears around 1980.
Style B′ is largely the same as B. The most notable difference is that it has a pair of facing trapezoidal holes cut into the base; see under base below. The reason for these holes is not known.
Such switches were made by Hirose in Japan. Hirose reported that they produced M6 switches in (or from) 1983 and M6 switches in (or from) 1985. Prior to this, they appear to have imported German-made switches, or the parts thereof.
There are only two confirmed instances of Style B′ switches in a finished product. The first is in the external extension to a Hirose Cherry B70-4753 (this section has no PCB and the bases of the switches can be seen). The main B70-4753 assembly itself also uses T-stem Style B or B′ switches, branded Cherry, and is dated to March 1985. While made in Japan, the extension area bears English legends.
The second is the control panel to the Amada SP-30 hydraulic press. eBay seller abc070506 offers M61-0100 switches as substitute parts for the M61-0120 switches in the SP-30. He also has one original Japanese-made M61-0120 in its original Amada packaging; he provided a photo showing that it, too, is Style B′:
(The text in the packaging reads: item name: keyswitch (“キースイッチ”), model number: M61-0120.)
These switches were also sold RS-branded with the Cherry branding crudely machined off. For some reason RS did not want anyone to know that these were Cherry switches. As they are not marked with the RS part numbers, it is not possible to ask RS for details on them, but RS part 338-765 has been found in Australia with the same defacing of the Cherry branding. These switches are Style A T stem, while 338-765 is listed in their records as M73-0120 (from after US switch production was discontinued), suggesting that the RS-branded Style B′ switches are M61-0120 likewise. Unlike the other examples, the Style B′ switches lack upper shell mould numbering.
The only example examined to date has thinner stationary contact metal (see under contacts below), which seems to be a cost reduction as the same change appears to have been applied to US-made switches. The internal structure of the base has a protrusion where the stationary terminal passes through to grip the thinner metal, and this provides extra support by keeping plastic between the trapezoidal hole and the terminal hole; it is almost as though the thinner stationary contact was a result of the effect of adding the extra holes, but this seems unlikely.
The base is also single pole only: the second set of internal support slots for the secondary contacts are not provisioned. However, Style B has also been found in this form.
Style C is the German design, used by the parallel Serie M7, with separate part numbers to the US-made switches. The top of the shell is matte finish, and bears a number at each terminal position. Previously these were assumed to be the terminal numbers (1 and 2 for SPST and DPST, and 3 and 4 for DPST only) but in fact the lid is placed on randomly, at least with the single pole switches. Even the US 1994 M7 brochure depicts M7 with the two SPST terminals marked 3 and 4.
The plunger core uses only a single design (instead of being different depending on whether straight or T mount was chosen), and with narrower dimensions it permits T mount switches to be double pole (not possible with the US-made switches).
Style C sometimes features a lockout hole in the plunger: this is a hole that passes all the way through the plunger just above the top of the shell. Switches with this hole are denoted Style C′. This hole is used to lock out keys by passing a rod through it, which stops the plunger from descending. At present, the chronological significance of this characteristic is not known. The only example of the lockout rod being present is in a Style D SAGEM keyboard, but a G80-0130 keypad with C′ switches has been found.
Style D is rarely encountered, being thus far only found in SAGEM Telex keyboards. It has prominent plate retention clips that appear to be able to be released from above the plate, and graphical Cherry branding. This is the only style which completely lacks circles on the top. Günter Murmann from Cherry concurs that these are M7 switches redesigned to SAGEM’s requirements.
The stationary contact design is roughly the same as Style C but it has two tabs that engage with the shell, instead of one; see below.
More notably, the keystem is Clare-Pendar mount, which may have been at SAGEM’s request to permit existing French keycaps to be used. The service documentation for the TX20 (which is what Style D seems to be from) gives the switches as Clare SF and SFL series. (No mention is made of Cherry switches.)
Style D switches all feature the lockout hole in the plunger seen in Style C′.
US-made switches were single throw, and supported single and double pole form and momentary and alternate action. The plunger of straight stem momentary switches provides two opposing pairs of cams to operate the switch contacts, with one or two contact pairs fitted as required. The size of the switch contacts combined with the size of the alternate action mechanism meant that alternate action switches could only be single pole, as the alternate action mechanism was placed where the second pair of contacts would normally be fitted. When the T stem was introduced, a corbel was fitted to the plunger to support the extra stem vane. This corbel occupied the space of the second stationary contact, restricting T stem switches to single pole momentary action; as a consequence, the second pair of cams were omitted from the plunger.
The German M7 switches allowed designs all the way up to quad-pole double-throw dual illuminated. The core of the plunger was a slimmer design that allowed a T stem in conjunction with two or more pairs of switch contacts. M7 switches also implemented dual half-width contacts, so that each side of the switch could support two contact pairs side-by-side. This allowed double-pole alternate action (with both poles on one side and the alternate action mechanism on the other), or quad pole with two contact pairs per side.
The diagram below shows the different plunger styles:
The chief visible difference between the original Style A and the later Styles AB, B and B′ is that the wall around the plunger aperture is offset by over half a millimeter. The reason for this change is not understood. Starting with Style B, the retention ramps were replaced with dedicated prongs. German M7 switches adopted a single plunger cross-section, cruciform in shape, that could be used for straight, T and cruciform keycap mounts. These differences in the plunger aperture are illustrated below:
Even the design of the base varies between US and German production. The base is 2.6 mm tall in US styles and 2.4 mm tall in German styles. In both cases, the base was ultrasonically welded to the shell, and it can only be removed using a knife.
German-made switches have standoffs over the unused terminal positions in single-pole switches. They also have a small inset area at the bottom.
As noted above, some switches have trapezoidal holes in the base; these are denoted Style B′. These switches were previously suspected to Japanese-made Hirose Cherry M5 and M6 switches, but recent discoveries of such parts in the United States (sold surplus and unidentifiable) casts doubt on this theory. Neither Peter Cherry nor Günter Murmann has been able to offer an explanation, and holes in the base of a switch seem illogical as manufacturers tended to seal the base of the switch against fluid ingress. There is good evidence to indicate that Hirose M6 switches took this form, but no evidence to indicate whether or not this form was manufactured in the US.
American and German switches use different stationary contact designs. The patents, from 1971 and 1972, show the stationary contact to be a solid rectangular sheet of metal. A transparent sample switch demonstrates that the stationary contact did originally take that form.
To save costs, the US and German factories each chose a way to remove some of the metal. The US design removes metal from the sides, with a characteristic triangular section at the top. The German factory removed metal from the centre. Due to the late introduction of these switches in Japan, no Hirose-made switches are likely to have the original contact design.
Style D stationary contacts have a slightly different top to Style C, with two raised blocks instead of one. The four known contact styles are depicted below:
Style A M61-0100 has metal around 0.8 mm thick. The Style B′ switches supplied by RS use noticeably thinner metal, as noted earlier, at around 0.5 mm thick, as do some American M61-0120 switches; this seems to be a cost-saving measure used both in the US and Japan applied after Style B was introduced, as Tom Hunter’s Style B switches appear to use the original metal thickness. German-made switches use stationary contacts around 0.77 mm thick.
The movable contacts are all very thin, typically in the region of 0.1±0.02 mm, although Ed Ferraton’s M73-0120 use thicker metal, closer to 0.15 mm. Ed’s also have a groove stamped into them in such a way that the terminal remains flat, while being less flexible than if the groove were not present.
The contact points differ between the US and German series. The US-made switches use Western Electric–style contact prisms with shoulders used for the assembly machinery. No German manufacturer could be found who could replicate this design, so German-made switches adopted a new design, of a purely triangular prism. These details are hard to see even with a magnifier, but more information is given on the contacts page.