"Wrist-turning pin" or "third form", characterised by the sword grip on uke's hand
Sankyo builds on ikkyo or nikyo (first and second form). It can be understood as a follow-up technique that is used if ikkyo or nikyo do not work.
The characteristic element of sankyo is to hold uke's turned wrist as you would hold a sword (grabbing the edge of the hand). Uke is led into the pin with a sword-like cut.
The sankyo pin is distinctly different from ikkyo and nikyo pins.