What type of wrench completely surrounds a nut or bolt head?

The correct choice is a box wrench, also known as a box-end wrench. This type of wrench is designed with a closed loop that fully encases the nut or bolt head, providing a secure grip on the fastener. The enclosed design helps distribute the force evenly around the fastener, reducing the risk of stripping or damaging the corners of the nut or bolt during tightening or loosening.

Additionally, box wrenches often have a specific size that corresponds to the fastener they are intended for, allowing for precise engagement and minimizing slippage. This makes them particularly useful in situations where access is limited or where a high degree of torque is required.

Other wrench types, such as adjustable wrenches and open-end wrenches, do not provide the same level of coverage around the fastener. Open-end wrenches can only grasp the flat sides of a nut or bolt and may slip under heavy torque, while adjustable wrenches have a movable jaw that allows them to fit various sizes, but they also do not enclose the fastener completely like a box wrench does. Socket wrenches do surround the nut or bolt head like box wrenches, but they are designed specifically to work with a ratchet mechanism.