Sansi is not a Jat clan but have historically been the ancestral book keepers for the Jats. They often are mistaken by uneducated people with the Sansi-Sandhawalia and other Jat clans with similar names.
It was nomadic tribe originally located in the Rajasthan area of northwestern India but expelled in the 13th century by Muslim invaders and now living in Rajasthan state as well as scattered throughout India. Historical records (over 900 years old) show they are not connected with other groups, called Sansi by coincidence, they are a completely different groups. 
- Thakur Deshraj, Jat Itihas, Delhi