Are these LEGO windows? I have had these windows in my LEGO collection since the 80's and my mum bought them second hand. They look and feel like Lego but don't have the word LEGO stamped inside the hollow circles on top.
These look like &quot;Blue-Box&quot; , a construction toy from Singapore
From inverso.pt


Blue Box basic elements with a 2X4 LEGO brick on the right



The inside of a &quot;Blue-Box&quot; construction set