Klein bottles, 1995.

Single surface models made by Alan Bennett in Bedford, United Kingdom. Four small Klein bottles (left to right): i) one loop relating to the single-twist Mobius strip, ii) two loop relating to the three-twist Mobius strip, iii) three loops relating to the five-loop Mobius strip, iv) four loop relating to the seven-twist Mobius strip. A Klein bottle is a surface which has no edges, no outside or inside and cannot be properly constructed in three dimensions.