this is a single joystick converter for the Spectrum +2 Grey and Spectrum +2/3 black only not for spectrum 128k or 48k/16k/+
it converts port 1 or 2 to atari / c64 standard from the amstrad standard wiring (amstrad changed the joystick ports on these models after acquiring sinclair in 1986)
the converter will allow you to use a better array of joysticks like the wico joysticks, competition pro and the even better zipstick

Zx Spectrum +2 +2a +2b +3 Grey/ Black Version Atari Joystick Converter Adapter