هم كالحلقة المفرغة لا يدرى أين طرفاها
They are like a seamless ring whose two ends cannot be identified.
The visible reference is a ring without a distinguishable beginning or end. When used of a group whose members cannot be decisively distinguished in precedence or merit, the resemblance is not simply circular shape. It concerns the difficulty of singling out one member from the rest.
Understanding the likeness requires moving from the physical image to an abstract relation. The example helps explain a subtle unstated respect: listing the ring's sensory properties alone does not recover the intended rhetorical meaning.