Various length telephone extension leads. 3 way are used for a standard BT telephone. 6 way are used for telephone systems as found in offices. If in doubt contact us for advice.
Telephone Systems (PBX's/Phone Switches) sometimes use extra cables, for this reason the 4 Way (431A) cables are not suitable. If the extension is required for anything OTHER than a standard BT telephone line/extension use the 6 Way (631A) cables.
6 way are backwards compatible with BT sockets that use 4 pins!