i think i can't totally understand the question.the floor in the pirates's set has a few convex rectangles where regular steck pieces fit.you can even fit a "normal" steck piece with 3 holes on its base (long rectangle/short square/long rectangle) a corner connector (solid base) and another "normal" one.everything fits.but when you try a bigger piece (a wider battlement) it is too long to fit the floor.when you join a "normal" piece with a corner connector on one side and on the other one a 180º connector and a corner one - you'll have the right dimension but the 180º connector doesn't have a hollow base and is unable to fit in the convex rectangle.system-x is so much better.if you want to know if the corner pieces in the pirates set are the same as in the 3666 - they sure look like it.