What tool is used to retrieve a drilling stem when the drilling cable has broken?

The correct tool for retrieving a drilling stem when the drilling cable has broken is the overshot. An overshot is specifically designed to engage with the outer surface of the drilling pipe or tools for retrieval purposes. It is slipped over the broken end of the drilling string and then pulled up to recover the tools from the borehole.

The design of the overshot allows it to securely grip the damaged or broken components, making it effective for this type of fishing operation. This tool is particularly useful in situations where the cable has failed, preventing further drilling and necessitating the recovery of equipment to continue operations safely.

While a combination socket, spear, and fishing jars are tools used in various fishing operations, they serve different purposes. For example, fishing jars are typically utilized to create shock or impact forces to free stuck tools, while a spear is designed to retrieve certain types of equipment or to engage with broken tools. These tools do not specifically grasp the uppermost portion of a broken pipe in the same way an overshot does, which is essential for recovering the drilling stem when the cable fails. Thus, the overshot is the most appropriate choice for this situation.