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Lo-Pro, also written LO-PRO, is a range of low-profile keypad switches from Stackpole. These switches are covered by three patents:

Patent Title Filed Granted
US 3767878 Keyboard switch 1972-09-21 1973-10-23
US 3924089 Keyboard switch 1974-08-28 1975-12-02
US 4119821 Normally closed switch 1977-09-26 1978-10-10

In Electronic Design magazine’s November 1972 Focus on Keyboards, LO-PRO is listed thus:

The latest Stackpole developments include a mode in which every key can be a repeat key without the need to depress a control key first and the LO-PRO, a new line of low-profile, mechanical keyswitches, designed for calculators and other low-throughput devices.

The switches are not depicted, but the description in the magazine fits well with the switch type whose patent was filed only a month prior. The type shown in the patent appears in a photograph in Electronic Design magazine’s October 1976 Focus on Keyboards, described only as Stackpole switches. There is no confirmation yet of what Lo-Pro switches are, but it is highly likely that the two types are the same.

In Computer Design in August 1976, the following advertisement was placed:

Compact, low-profile keyboards, for calculators, POS devices, and data entry equipment, may be designed with Lo-Pro 5 or wobble-free Lo-Pro 20 keyswitches. Both are available in a high-profile configuration as well. Low-Pro 20 and its high-profile equivalent have integral elastomeric cushions to increase error-free operations to 20 million. Std coding, such as ASCII, is available, while variations can be ordered. Engineering assistance can also be provided.

Again, this is not illustrated. The “elastomeric cushions” appear to refer to the “electrically conductive elastic members” found in the second patent, which are little caps on the ends of the contact spring. Possibly Lo-Pro 5 is the original 1972 design (with a five million cycle lifetime) and Lo-Pro 20 would be the 1974 design with an extended lifetime, although the 1974 design does not seem to have any additional characteristics that would make it more stable.

Although not targeted primarily towards alphanumeric keyboards, they can be seen inside the Netronics Professional ASCII keyboard. There is also an unidentified keyboard with a different variant of Lo-Pro switch; this keyboard has the same brand of keycap as used by Mechanical Enterprises, and the same typeface.


KS-200 is a switch array system, which is likely to be Stackpole’s standard pre-DIN switch grid system (see Stackpole switch grid on the Deskthority wiki). The typical lifetime per switch is given as 20 million cycles. KS-200 can be seen advertised in Computer Design in April 1981; see Documentation below. KS-200 keyboards could be ordered with or without keycaps, and with or without a PCB. KS-200 keyboards are described as non-encoded. The advertisement depicts a complete array (albeit too dark to make out), smaller arrays for function keys and number pads, and a single switch.

The arrays were intended provide keycap alignment (ensuring that keycaps are not crooked) and to remove the need for PCB stiffeners. (PCB stiffeners are rare, but Datanetics made use of them, and they can also be seen in some Apple II keyboards.) As there is no mounting plate to secure the switches, the arrays and single switches are affixed to the PCB with screws. Although it would be possible to form a keyboard from single switches, such an endeavour would be fairly pointless, and the discrete switches may be too large (without the shared walls) to fit into a ¾″ layout.

According to D’Milo Hallerberg from Hi-Tek, KS-200 was ultimately based directly on Hi-Tek High Profile, a move that led to failed legal action on Hi-Tek’s part. There is evidence to suggest that Stackpole’s original copy was closer in design to Hi-Tek’s, so KS-200 may represent the revised design with opposing pairs of identical contacts (one side solid, one side bifurcated) rather than Hi-Tek’s pairing of solid and quadfurcated contacts. The technical merits of Stackpole’s redesign require engineering understanding, but it did have the benefit of simplifying inventory and manufacturing by requiring only one contact part. This contact design would continue to be used in their later mechanical types.

Three patents are known for the high-profile array system. The first patent describes the type seen in an HP 2623A keyboard. This type uses one solid contact and one fingered (slotted) contact, just as with Hi-Tek High Profile. The characteristic stepped separator bar is also clearly depicted. The second patent shows the replacement dual bifurcated contact system, where both contacts within the switch are identical. A tactile type was also patented, which has yet to be encountered.

Patent Title Filed Granted Covers
US 4255635 Keyswitch 1979-09-17 1981-03-10 This appears to be the original array system, with separate solid and fingered contacts
US 4342892 Keyswitch 1980-08-08 1982-08-03 KS-200 array system with the matching dual bifurcated contacts
US 4361743 Lost motion keyswitch 1981-03-06 1982-11-30 Tactile version with hysteresis; uses the dual bifurcated contacts

Of the three patents, only the second one was transferred to Illinois Tool Works, in 1987.


Advertised in 1984, KS-200E is a DIN-compliant array system, replacing KS-200. The “E” in both this and KS-500E may stand for “ergonomic”, in relation to DIN compliance.

KS-200E uses a “sturdy monolithic housing that assures keycap alignment”, but it also offers “discrete switches or arrays”. The magazine advertisement depicts the a keyboard with PCB-mounted “interlocking” (“puzzle piece”) switches, which appears to be their discrete switch option. As these have been found in a Lear Siegler ADM 11 keyboard alongside switch grids, it would appear that the low-profile grids are the monolithic form of KS-200E.

Typically, these keyboards are array based, but there is one known type—VTD 52S—that uses the interlocking switches for the alphanumeric area. These switches, which are an unusual colour and roughly moulded, are not proven to be legitimate, although the keycaps are also a match with those from a confirmed Stackpole keyboard.

The rated lifetime for KS-200E is 50 million cycles.


KS-500E is the companion membrane technology to KS-200E, advertised at the same time in Computer Design magazine. Like KS-200E, these are DIN-compliant. The rated lifetime was given as 10 million cycles in September 1983, and 20 million cycles in February 1984. Bounce time was given as under 1 ms when new, and 5 ms maximum at end of life. Travel is 0.140″ (3.6 mm).


KS-600E is a keyboard family using plate-mounted, discrete switches based on Stackpole’s existing switch design. KS-600E switches have 0.140″ (3.6 mm) travel, and like KS-200E are rated for 50 million cycles. These switches can be either linear or tactile, and Stackpole offered them for sale separately.

The switch is pictured in a magazine advertisement from August 1984. The excessive JPEG compression makes the switch design hard to discern, but it is not dissimilar to the linear switches used in the Zentec Zephyr DD/ID220 manufactured in August 1985, and this keyboard may well be from the KS-600E family.


All of the Computer Design material was scanned by Bitsavers.