These are square and triangular blocks with bevelled projections on two sides and matching bevelled slots on two others to allow blocks to slot together (see third picture below). Earlier blocks were in wood but later they were made of hollow plastic in red, white and blue.
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 other construction methods
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| materials | wood, later plastic |
| date | 1930's-50's? |
| made by | Wood Products Manufacturers, Detroit Michigan, USA; then Hillcraft Industries, Traverse City, Michigan, USA |
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