Some of the 2x4 Duplo castle pieces fit onto Quatro because their stiffening plates are set much deeper within: (URL) Duplo Brick 3 x 4 x 2 with Machiolation> The (URL) 4777 Knight's Castle> (URL) comes with> three (URL) enourmous Duplo plates> (...) (18 years ago, 26-Jul-06, to lugnet.quatro, FTX)
