Final answer:
The Jacobs chuck shank is the type of shank with a small groove for locking into the contra angle attachment in dental procedures.
Step-by-step explanation:
The type of rotary cutting instrument shank that has a small groove at the end and locks into the contra angle attachment is known as the Jacobs chuck shank. This design allows for a secure fit when the instrument is being used in dental procedures, ensuring stability and precision. Other types of shanks such as the straight shank, friction grip shank, and tapered shank do not have this specific feature for locking into contra angle attachments.