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ETL 18 is a mechanical switch series branded ITT and marked as being made in West Germany. The switches are officially named “ETL 18” with a space, but they are elsewhere universally referred to as “ETL18” including by surplus parts stockists. German patent 3140199 covers this series; it was filed by Rudolf Schadow GmbH in October 1981. This patent was complemented by US patent 4514609 “Pushbutton switch having leaf-shaped contact spring” filed in September 1982 by ITT Industries, Inc.

The date of introduction is not known, due to the lack of contemporary information. An advertisement in Schweizerische technische Zeitschrift from August 1981 (no. 17, page 720), partially accessible on Google Books, notes: “Messeneuheiten von ITT in Stichworten: Alphanumerische Keyboardtaste ETL 18 und kleinste Eingabetaste mit LED von Schadow; Radiallüfter für die Elektronikbelüftung …” This advertisement suggests that ITT already owned Rudolf Schadow at the point that the switches were introduced, as suggested by the US patent. A label on a carton of 100 switches provided by Ellison Electronics—who carry surplus switches in stock—shows that the switches in question were manufactured by ITT Schadow in Germany in March 1993. C&K, now the owner of ITT’s switch product range, reports that ETL 18 went obsolete at the end of the 1990s.

The triangle+circle logo on the switch is that of Schadow, as shown in an IEE advertisement in Electronic Engineers Master 1971–72, volume 2, pages 1922–25:

There is virtually no trace left of Rudolf Schadow GmbH itself, and the company is overshadowed by the German sculptor of the same name, after whom the manufacturer may have been named.

ETL 18 is not commonly encountered. They have been found in one or two control panels, as well as one of the keyboard types used with the Interact Model One computer.


ETL 18 is highly unusual in terms of both its implementation and feel. The return spring sits horizontally across the switch and appears to offer some form of over-centre action. The result is that the force decreases up to the actuation point instead of increasing, which can be seen in Jacob Alexander’s ETL 18 force curve, which is recreated below:

This implementation achieves friction-free tactile feedback that is much smoother and more precise than Mitsumi’s KCT and KLT horizontal spring types. The cost of this superlative feel is the comparatively high bulk of the switch, possibly due to the required length of the internal spring and contact bar.

The switch is surprisingly large considering its age: coming onto the market at a time when the DIN ergonomics standards were on the horizon, ETL 18 is too large to meet the 30 mm keyboard height requirement. The overall switch height is 27.2 mm, leaving only 2.8 mm for the keycap above the keystem and for the bottom of the keyboard. This may account for the extreme scarcity of these switches in keyboards.

The keycap mount dimensions are given in the 1986 catalogue as follows:

Product range

The 1986 catalogue lists the following products within the range:

ETL 18 options
ETL 18 SPST-NO momentary, no diode
ETL 18 S SPST-NO momentary, diode
ETL 18 EE SPST-NO alternate action
ETL 18 La SPST-NO momentary, integrated LED
ETL 18 Lb “Fixing device for the attachment of a separate LED”
ETL 18 SB “Accessories for space bar mounting (without spacebar button).”

The ordering details in the catalogue are not clear. The following two LED combinations are named:

ETL 18 Lb is suggested to be simply a clip-in tube that affixes the LED to the mounting plate, while ETL 18 La has the LED mounted inside the switch. The sole ordering code example gives “ETL 18 - EE - La - Red” for a red LED–illuminated latching type.

Red, green and yellow LEDs were available.

In most cases, the basic momentary switch is encountered. eBay listing 303950204739 “5 x ITT ETL18 Schalter” depicts the momentary type as well as some form of alternate action illuminated. The rear left corner of the latter switch appears to have a vertical spring for the alternate action mechanism, and there appears to be a metal pin between this assembly and the plunger. The far right corner appears to have a facility for attaching an LED, although the catalogue shows that the LED is fitted onto some kind of stand rather than directly onto the switch itself.

The ITT Switches Programme 1986 depicts on the cover both black and white plunger variants, with no known explanation.


ETL 18 specifications
Total travel 3.5 mm
Latching travel 2.5±0.3 mm (ETL 18 EE)
Pretravel 2±0.3 mm (standard)
1.7−0.3 mm (ETL 18 EE)
Operating force, “initial” 50±10 cN
70 cN max. (ETL 18 SB)
Operating force, end of travel 80 cN max. (standard)
100 cN max. (ETL 18 EE, ETL 18 SB)
Operating force, actuation Less than or equal to the starting force
Contact material “Au”
Switching power 3.5 W max. AC/DC
0.02 mW min. DC
Switching voltage 28 V max. AC/DC
2 V min. DC
Switching current 125 mA max. AC/DC
10 µA min. DC
Rated lifetime, 5 V at 1 mA 20 million cycles (standard)
50 thousand cycles (EE and La versions)
Rated lifetime, max. switching power 1 million cycles (standard)
50 thousand cycles (EE and La versions)
Contact resistance 50 mΩ max. (new) 1 Ω max. (at rated lifetime)
Contact bounce 5 ms max.
Minimum spacing 19.05 mm


The following material was provided by C&K EMEA and represents their only known material on this switch series.

See also