A stud wrench is a special tool used to fit threaded studs into a plate of metal that can then have bolts attached to the free end to secure two items together. In order to screw a threaded rod into a metal plate a usual spanner would not work as the rod has no head for the spanner to grip and a traditional set of pliers could damage the threads. A specialist tool was therefore used that gripped the rod, protected the threads and gave the torque needed to screw the stud in. These tools have to be sized exactly to the rod they will be used with to work effectively and today we are looking at a particularly large example used by the British Army:

The head of the tool has a hole through which the stud can be passed:

A swinging, serrated tip is pressed into the stud when the handle is pulled and this grips it whilst it is rotated into place:

The shaft of the wrench is marked with a /|\ and the sizes of studs the wrench could be used with, in this case 5/8” and ¾” studs:

The only other marking is the number 197 stamped onto the head:

The wrench is particularly large and so would be used with large studs such as those used on truck or tank engines, large locomotive cylinders and other particularly large pieces of machinery.