Museum of Plugs and Sockets logo, small Classic continental European
plugs with different pin designs
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Nearly all plugs have at least two, straight pins. However, very different models of pins have been designed. Two examples are shown below. One plug has two sharply bent blades, the other has a single pin that consists of two concentric conductive elements.


Hakensteckdose, Hakenstecker Hakensteckdose, Hakenstecker
Hakensteckdose, Hakenstecker

1 - 3
Surface mount, black glazed steatite wall socket and matching plug. The plug has 6.7 mm wide rectangular bent blades. These  plugs and sockets, made in Germany, were referred to as Hakenstecker and Hakensteckdose (hook plugs and sockets). Image no. 3 shows the socket without top half to illustrate blade-socket contact.
A 1930 wholesaler catalog mentions hook plugs and sockets as devices for special electricity tariffs.   {WN}

The origin is unknown; as yet the GTR logo has not been traced. It is likely that hook plugs have been used mainly (or only) in Thüringen and Sachsen. The shown specimen, rated at 6A - 250V, is an early model, probably made in the mid or late 1920s.

Also 10A models have existed. Hook plugs remained in use - at least until the 1960s - in the former German Democratic Republic. The image no. 4 shows a GDR made 10A hook plug. The size of the Bakelite cast is comparable to 'standard' plugs with two round pins.  Blade width is 6.5 mm; spacing is 15 mm (center to center), identical to the 6A porcelain plug. The 10A fits in the 6A porcelain socket.    {RH}

Plug has a grade 1 TGL quality mark and has been made by IKA (VEB Installation, Kabel und Apparaten in Leipzig). In 1958 IKA became a part of a larger conglomerate based in Ruhla, Thüringen (EIR = Elektroinstallation Ruhla).
Hakenstecker 10A made in GDR


Concentric plugs, 4A and 6A Concentric plug and connector, 6A

Maeler & Kaege 10A concentric plug Concentric socket

5 Plugs with two concentric contacts and housing made of Lignum vitae wood. Concentric plugs have been made in Germany from early 1900s until mid 1960s, mainly for more demanding, outdoor use. In Germany they were known as Garagenstecker or Zentralstecker. Shown examples and images in catalogs show they were often equipped with a watertight locking sleeve. Occasionally they were also offered for domestic use (see no. 9).
Versions existed that were rated at  4, 6, 10, 15 and 20 A. Wooden and ebonite plugs have been made until late 1920s. None of the wooden examples in the collection have a manufacturers name or logo.   {WN}
6 Concentric 6A connector and plug.   {WN}
7 Waterproof concentric plug, rated at 10A - 250V. The lower image shows the inner part with wire connections Cast has Bakelite MPAD mark MU-51. Maehler & Kaege in Ingelheim am Rhein (MU) has made the press work, and probably the complete plug. Type 51 stands for phenol or cresol resin reinforced with cellulose. Dating: 1950s.   {WN}
8 The museum collection doesn't have a classic concentric socket. The image shown has been copied from a 1937 Siemens catalog. It shows a brown Bakelite 10A flush type socket. It a typical domestic product. Sockets for heavy duty or outdoor use were made of cast iron or a robust quality Bakelite.

Porcelain plug with 5.6 and 4.4 mm slots Concentric plug with porcelain socket
Ring of concentric plug indicating 4 Amp 250 Volt

Concentric plug wiith cord and switch  

9 Concentric plug with black glazed porcelain outlet found at the attic of a 100+ years old stately home in Rotterdam, Netherlands. Plug and pin dimensions are similar to plug no. 5 (top model). The brass ring to secure the plug indicates a 4 Amp 250 Volt rating.
The outlet has contacts with a diameter of 5.3 mm (left) and 4.1 mm (right). Matching plugs were, among others, made by Stotz-Kontakt (see order no. 14353). It seems likely that this combination of plug and outlet was designed for a special purpose; similar devices have not been found in catalogs. Manufacturer is unknown.   {YG & FS}
10 Besides plug no. 9 also a similar concentric plug with cord and push button was found. It has a 4 Amp. 250 Volt engraving, identical to image no. 9c. Using the device with the same concentric socket that was required for plug no. 9 is asking for troubles. The fact that two identical devices could be used for fully incompatible purposes is remarkable, and indicates that they are exclusively designed for specific types of desks or cabinets.   {YG & FS}

WISKA socket for concentric plug
WISKA socket for concentric plug
WISKA concentric socket and plug

WISKA concentric plug
WISKA concentric plug and connector

It is remarkable that concentric plugs and sockets, essentially identical to the wooden Garagenstecker (image nos. 5 and 6), are still in production. They are nowadays used for marine applications. Material shown in image nos. 11 - 15,  made by WISKA (Kaltenkirchen, Germany), has been delivered by the Dutch WISKA representative Rometel Trade B.V.
11, 12
Concentric, polyamide, surface mount socket, rated at 10A - 50V. Image no. 11 shows the IP 56 watertight socket with closed screw cap; images no. 12 shows the concentric contacts.
13, 14
Socket and matching 10A - 50V, IP 56 plug. Compare the pin sizes with 6A - 250V wooden plug (image no. 5).
15 Despite ca. 100 years difference in age, the WISKA plug fit perfectly in a wooden 6A - 250V connector. Even dimensions and screw thread of the brass locking collar have not been changed.


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