The 40 piece STEM learning educational construction tiles set can be used either as a stand alone magnet tile kit or in conjunction with other PicassoTiles magnetic building blocks as add-on sets. The tile-set has been updated with stronger and improved magnets that have the strength to easily hold up to 8 square pieces together in a large chain. Swappable Magnetized Clip Ons: The magnetic set comes with 16 magnetic tiles, 8 windows, and 16 clip-in doors that can attach onto each square tile. Changeable clip-in inserts allow for kids to build bigger structures with operable windows and doors perfect for any princess castle, dream house city building, farmer's barn, skyscraper or whatever construction buildings your child can creatively imagine. Creativity beyond imagination, create and engineer limitless varieties of castles, mansions, skyscrapers, towers, farms, shapes, animals, and more! In The Box: 16 clear magnetic tiles 8 window clip-in pieces 16 door flap clip-in pieces