When comparing these Circular Connector Contacts like 27961-15T9, 27961-15T12 and 27961-15T112, from ITT Cannon LLC, the only difference is with the added T9, T12 and T112 suffixes.
These suffixes call out the plating on the contacts.
T9 = Silver Finish
T12 = Standard Gold Finish
T112 = Heavy Gold Finish
Click here for the Datasheet. This information is located under General Specifications at the bottom of Page 7.