Compared with LEGO bricks on top.

PUWI, later PUWI BLOK, was made by Paul Willumsen in Denmark during the 50's and 60's. The name was made with two letters from Paul's first and last name. As it is frequently found together with LEGO bricks from the same period it appears to have been a solid competition for LEGO.

PUWI was also exported and sold in other countries. The same name was used for Norway and Sweden. However in some European countries the name "Diplom" was used for the bricks. In the US "LINO Method" was used. It could very well be that an own production was set up in the US, and/or that the rights were sold to a US company.

PUWI started out with simple hollow bricks with slots as the LEGO Automatic Binding Bricks. At some point extra support was added underneath the bricks which also worked to increase the clutch power between the bricks. It is likely this happened around the time LEGO came up with the tube system in 1958.

Also check out this website about the same brand for more information and pictures: Inverso.pt