I had a set of these Galt Playplax pieces when I was a kid, and I swear not a week goes by that I don’t think of them. As a child, there was something super magical about them, and I remember spending hours building with them, then peering through the kaleidoscopic towers of rings and squares I'd constructed, studying how the colors merged and the shadows they cast (I recommend using these on a white table!) Now that I have a set in hand some 40 years later, I’m still completely taken with them! And they are extremely fun to photograph!
In the interim, vintage sets like this seem to have become quite collectible. They were designed by Patrick Rylands in 1966 and made by the British company Galt toys, with a number of different versions produced over the years. I’d say this is the best among them, combining both rings and squares (some sets just included rings, and some just squares) and it is also from what I’ve found the rarest, dating to 1983. (I can find no other editions of this set for sale out there at all, and only one documented as sold by a British seller some time ago.) This set is entirely complete, with 12 interlocking rings and 72 square plaques, in four colors, all of which interlock.
Wear to the box and lightly used, but in very good condition with no cracks or chips or major scratches that I can see. Box measures 13 1/4” l x 10” w x 2 1/4” t. Individual squares measure 2" x 2".