Day and Night are the rotations of that wheel. It is encircled by heat and cold. Pleasure and pain are its joints, are hunger and thirst are the nails fixed into it.
अहोरात्रपरिक्षेपं शीतोष्णपरिमण्डलम्। सुखदुःखान्तसंश्लेषं क्षुत्पिपासावकीलकम्॥