Bus doubler for ZX81 or ZX Spectrum.

The passed through busses are Specci-wide, but the connector to the computer is only ZX81-wide. So you could use it for the ZX81 or for the ZX Spectrum, but only to attach extensions with a narrow connector, e.g. the Sinclair printer or many joysticks. Items which required all lines of the ZX Spectrum bus could not be attached.