A cylindrical brass bore inspection gauge, likely British military issue, designed for checking barrel wear and internal bore dimensions of service rifles and machine guns. These precision tools were used by armourers to ensure a weapon’s barrel remained within operational tolerances, thus maintaining accuracy and safety. The example shown retains its original patina, with a threaded end cap possibly for an interchangeable gauge head or cleaning mirror. Such items were standard in armourer’s toolkits from the mid-20th century and were essential for maintaining weapons in both field and depot conditions.