Editing SMK J-M0404 series (section)

==Variants==
===Low friction===
The low-friction variants use a blue-white viscous substance painted onto either side of the slider. These switches use brown sliders, and are intended for wider keys. The objective of the lubricant appears to be to reduce binding when hitting wider keys off-centre.

The "low friction" designation comes from Apple service documentation.<ref name="Apple" />

<gallery widths=250 heights=187>
File:SMK J-M0404 slider comparison.jpg             | Standard vs low friction sliders
</gallery>

===Low force===
Low force switches use weaker springs. These switches are indicated by a cream or beige base. One use of these is for the return key in some [[Acorn BBC Microcomputer]] keyboards, where instead of a single switch and a stabiliser, a pair of low force switches were used. Currently no photographs are known to exist of the various SMK switch arrangements in the BBC Micro, which differed between batches.

The angled keystem low force switch has been found with both beige and ivory bases. The beige base version examined has a 16.5 mm long spring with a wire gauge somewhere between 0.18–0.20 mm. The ivory base version has a shorter, 15.6 mm long spring and 0.19 mm gauge wire. There is no readily discernible difference between the two switches and it is unclear whether the use of two separate colours is significant or whether SMK were not fussy about the shade.

<gallery widths=250 heights=187>
File:SMK vintage linear, low friction variants.jpg | Low friction uses a brown slider, and low force (right) uses a beige base
</gallery>

===Dummy switches===
Both sprung and unsprung dummy switches were used.

<gallery widths=250 heights=187>
File:SMK J-M0404 low-friction dummy switches.jpg   | Sprung and unsprung low-friction dummy switches from BBC Microcomputers
</gallery>

===Keystem===
The keystem can be either short or tall. Short keystems can be upright (straight) or angled. Tall keystems are rare and so far only known from Apple keyboards; tall angled keystems have yet to be seen. Possibly to allow the slider to be inserted into the shell, the "inner" vane of angled keystems is tapered away at the top.

===Known variants===
The table below shows all discovered variants. There are far more possible combinations than have been discovered. For example, tall stem angled has never been seen, and the tall stem switches have not been found in the same number of varieties as short stem switches.

{| class="wikitable variants-table"
! !! Part !! Description
|-
| [[File:SMK J-M0404 standard -- variants table.jpg|175px]]                        ||  || Short stem, upright
|-
| [[File:SMK J-M0404 tall -- variants table.jpg|175px]]                            ||  || Tall stem, upright
|-
| [[File:SMK J-M0404 low friction -- variants table.jpg|175px]]                    ||  || Short stem, low friction
|-
| [[File:No photograph.svg|175px]]                                                 ||  || Tall stem, low friction
|-
| [[File:SMK J-M0404 angled -- variants table.jpg|175px]]                          ||  || Short stem, angled
|-
| [[File:SMK J-M0404 low friction angled -- variants table.jpg|175px]]             ||  || Short stem, low-friction, angled
|-
| [[File:SMK J-M0404 low friction light angled -- variants table.jpg|175px]]       ||  || Short stem, low-friction, angled, low force
|-
| [[File:SMK J-M0404 low friction light angled pale -- variants table.jpg|175px]]  ||  || Short stem, low-friction, low force, angled, pale version
|-
| [[File:SMK J-M0404 low friction light angled dummy -- variants table.jpg|175px]] ||  || Short stem, low-friction, low force, angled dummy
|-
| [[File:SMK J-M0404 low friction dummy springless -- variants table.jpg|175px]]   ||  || Short stem, low-friction springless dummy
|-
| [[File:No photograph.svg|175px]]                                                 ||  || [[SMK J-M0404 alternate action|Tall stem, upright, latching]]
|-
| [[File:SMK J-M0404 alternate -- variants table.jpg|175px]]                       ||  || [[SMK J-M0404 alternate action|Short stem, upright, latching]]
|-
| [[File:SMK J-M0404 stemless -- variants table.jpg|175px]]                        ||  || Stemless
|-
| [[File:SMK J-M0404 illuminated.jpg|175px]]                                       ||  || [[SMK J-M0404 illuminated|Short stem, upright, illuminated]]
|}

SMK-branded parts in this series appear on a number of websites, typically with bogus stock figures (as high as 65,000 per part), but attempts to determine any correspondence with known switches has proved futile. The following parts are confirmed (with corrections for transcription errors such as "(SHARP)" or "≠" for "#"):

{| class="wikitable"
! Part no. !! Description !! Source
|-
| J-M0404#01 || SWITCH                       || Abtronics
|-
| J-M0404#04 || Switches                     || Jotrin
|-
| J-M0404#05 || PCB Single Keys[witch]       || ISO Parts
|-
| J-M0404#08 || KEY SW MECH BTTM SEALED 5AMP || ICLocator
|-
| J-M0404#10 || PCB Dummy Keysw[itch]        || ISO Parts
|}

No Abtronics branches in any country ever respond to enquiries, and they have a high minimum order value; ISO Parts and Jotrin list bogus stock of nonexistent parts. Obtaining these parts may not be possible. Only J-M0404#10 may be identifiable, as it likely refers to the dummy switch sometimes found under space bars (e.g. some Type 2 [[Acorn BBC Microcomputer]] keyboards, and the [[SMK J-M 9031]] keyboard).

Abtronics also lists J-M0409#01 with description "REF.042R" and no manufacturer; it is conceivable that the angled stem or tall stem versions were covered under a related series, but J-M0409 series may not exist. Retroamplis sell [http://www.retroamplis.com/Boss-spst/en part JM-0404], intended for Boss pedals, which is a standard short straight stem switch. This apparently incorrect part number is derived from Boss, as noted in the [http://musicthing.co.uk/modular/?p=1113 Boss PS-2 Schematic] (under "SWITCHES", as JM-0404 "Key Switch").