Hi-Tek and Stackpole recognition
Particularly in the earlier years, Hi-Tek Corporation frequently supplied bare Hi-Tek High Profile switch grids to computer and equipment manufacturers and left the customer to provide the keyboard controller and circuitry. The supplied switch grids were typically left unbranded. Stackpole copied Hi-Tek's switch design, resulting in a failed lawsuit for patent infringement. An HP 2623A keyboard found with yellow sliders suggests that Stackpole did copy the 1+4 finger arrangement of Hi-Tek, yet even this keyboard uses switches with designs that follow Stackpole patterns.
It is possible that the legal action on Hi-Tek's part resulted in Stackpole changing the contact finger design to the rotationally symmetric 3+3 arrangement (which they patented), but this may have been an evolution of their product range that would have occurred regardless.
Stackpole-made keyboards are much more likely to bear a Stackpole-branded PCB, and later on Hi-Tek also produced full keyboard internal assemblies with branding both on the switches and the PCB.
According to former Hi-Tek employees, Hi-Tek sliders were considered to be always colourless. However, black sliders are confirmed to exist, both separately and sharing a keyboard with colourless sliders. In later keyboards, however, the sliders do appear to be typically colourless.
Many of these types of keyboards use yellow or green sliders, and where these are not marked with a switch manufacturer, it seems fair to assume Stackpole as the manufacturer. Indeed, all such examples also have physical characteristics identifiable with confirmed Stackpole keyboards.
- Yellow (typical)
- Green (common in microcomputer keyboards)
- Colourless (typical)
- Black (common in old terminal keyboards)
There are several distinct differences between the two companies' switches. The parts to examine are:
- The waffle frame if present (a flat-top grid will most likely be Hi-Tek)
- The separator bar that holds the contacts apart at rest
- The shape of the switch contacts
The separator bar in Hi-Tek switches appears to be universally wide with fully straight sides. The left contact is solid, and the right contact is split into four fingers. In most keyboards, the momentary switch slides have thicker and taller corners; this is not universally true, and alternate action sliders all appear to omit this design.
Stackpole standard profile
The most distinctive characteristic of Stackpole switch grid switches appears to be the "boss", the T-shaped portion of the centre vertical wall leading to the slider guide shaft. These appear in all standard profile Stackpole-branded keyboards, and never in any Hi-Tek branded keyboards. This alone appears to be a firm indicator of Stackpole switches, and is true regardless of switch profile or contact design.
The separator bar is much narrower than with Hi-Tek sliders, and it is held by projections at each end, giving the bar a stepped appearance and the holes in the slider a characteristic shape.
Typically, Stackpole switches have rotationally symmetrical contacts, each one having one wide and two narrow fingers; this contact arrangement likely results in simplified production. In standard-profile switches, the visible portion of the contacts are also wider in the direction perpendicular to the separator bar relative to those of Hi-Tek switches.
An HP 2623A keyboard has been found with the Hi-Tek-style 1+4 finger arrangement; even so, all other characteristics are a match for Stackpole including the slider colour, the waffle frame boss, the deeper contacts and the thin separator bar.
Stackpole low profile
Stackpole also made a low-profile version of the switch grid where the waffle frame is almost flat. These switches are entirely distinctive due to the revised slider design. The contacts are still rotationally symmetric, but they are shallow perpendicular to the separator bar as per Hi-Tek switches.
Stackpole interlocking appears to use an identical slider and contacts to the low-profile grids.