When the Palms in Ardhachandra mudra touch each other vertically and horizontally we get the Chakra Mudra. The right palm is vertically held and the left palm is horizontally placed over the it.

Lets tale a look at the viniyoga shloka (uses)
chakrarthe viniyujyaate
It says that this Mudra denotes a Wheel. In Sanskrit Chakra means a circle [...]