Hi @AnnaFless and @chaiwanhao . For a contact on SimScale you always have a master and a slave assignment. For every slave node one searches for the nearest master element. If no position tolerance would be active, all slave nodes would be bonded to their respective master element. If a position tolerance is active, only the slave nodes would be connected to their master element, if the distance is below the position tolerance. The automatic setting takes as tolerance value 1/10 of the characteristic element length on the slave surface in the manual setting the user defines the tolerance value.
So if your slave surface is on the cylinder and the cylinder lies exactly on the other part, every tolerance value will result in the same since all nodes will be connected.
On the other hand, if your master would be on the cylinder, you should definitely activate a position tolerance since you only would want the nodes “close” to the cylinder being connected to it.
I hope this answered your question, I’ll be here if you need more assistance.