Probably due to having different brand tracks but it was very tight on the male side and kind of hard to remove. Could use a little more length as a slight gap wouldn't hurt. It still works and fits the big Lego blocks perfectly.

The piece fits the duplo perfectly, but the out end of the piece is hard to fit in.

Love anything that takes two incompatible brands or items and makes them work together. My nephews are going to love this!

Nice design