This is blocking puzzle pieces. They fit together like a puzzle, and are perfect for blocking any size or shape of knitting or crocheting. There are 9 pieces to each set. You just add a piece of the puzzle where needed (such as sleeves for a sweater).
I used these to block the little white sundress, and it worked out perfect. I blocked the sweater on the puzzle pieces on the kitchen counter, then moved the whole thing, intact, to the floor in the bedroom. I just love them, and wonder how I got along without them all this time.
They are available for sale at knitpicks.com