Oh yes, they seem to be out of this world now, but these two-wire, bayonet-mount connections were in widespread use several decades ago.
In those days, the now-ubiquitous 3-pin power outlets and plugs were unheard of. There was no such thing as Earth wire or connection. Electrical appliances (though few families could afford them) were DIY-retrofitted with bayonet-mount, two-pin plugs (made of phenolic thermosett plastic).
Of course there were plenty of occasions when branching was required, and for such, 2-way and even 3-way sockets enormously popular, coupled with plugs to which the classical Black & Red* twisted cables were attached.
*Note : In case younger folks do not know, Black=Neutral, Red=Live. Of course, nowadays, Neutral=Blue, and Live=Brown.
Hope this post reconnects many who are still on this earth to some power memories.