connectors Various miniature versions of the banana connector have been introduced. One type is 2.6 mm in diameter and about one third the length of the standard connector, and is commonly used in model railway applications. These are substantially more fragile than the larger connectors. Multiple miniature banana connectors are usually spaced on inch centers. Another miniature type is the 2 mm banana connector, which is otherwise identical to the 4 mm version, including the various plug contact styles and availability of sheathed versions for high voltage applications. Pin tip jacks A closely related but different design is the so-called "pin tip plug" and matching "pin tip jack". The pin tip plug designs resemble banana plugs, but without the spring on the male pin. The diameter of the male pin is 2 mm. Instead, these designs rely on spring action in the female jack, or tightly machined tolerances, to ensure good contact. The pin tip plug design was used where maximum density of connectors was desired (such as in pin plugboards), or a very compact connector was needed. Wander plug These superficially similar plugs were widely used in the UK and elsewhere until the 1960s. A significant use was for connecting the separate HT (High Tension, usually 90 Volts) and grid bias batteries in early battery powered valve (tube) radios and for the antenna and earth (ground) connections and external loudspeaker in both mains and battery powered valve radios. The battery terminals were short (approximately 6 mm to 10 mm) bell-mouthed brass tubes of nominal internal diameter. The wander plug may have gotten its name from its need to "wander about" when setting the correct grid bias voltage(s) for most economical operation of the radio. The wander plug was always used in a rigid socket and therefore the pin end was split to allow some elasticity and provide a secure fit in the socket. Often a machined brass component which formed the pin contact (which was split) and the means of connecting the external wire, clamped by means of a screw-on coloured hard plastic cap. Another design used an actual split pin of plated steel, the parallel ends of which formed the plug tip. A machined brass component with an internal bore of just over inch, a transverse slot to accommodate the eye end of the split pin, and an external screw thread to engage the coloured hard plastic cap,