Klein bottles, 1995.
© Science Museum / Science & Society Picture Library
Single surface models made by Alan Bennett in Bedford, United Kingdom. Three toroid single surface vesels, one with the loop inside the torus, one with a narrow loop outside and one with a wider loop outside. All can be cut to produce a pair of single-twist Mobius strips. A Klein bottle has no edges, no outside or inside and cannot be properly constructed in three dimensions.