45mm

45 millimeters (45 mm) is a unit of length in the metric system. It equals 0.045 meters, or 4.5 centimeters, and about 1.77 inches. The term is commonly used in technical specifications to describe a size or dimension, typically the diameter, width, or length of an object.

In engineering and manufacturing, 45 mm appears as a standard size for components such as bores, shafts, holes, or bushings. It is a practical dimension in assemblies where a precise, moderate size is required.

In consumer products, 45 mm is a common diameter for circular parts. It is found in items such as watch cases, camera filters, and certain lens elements. The 45 mm size may also correspond to the outer diameter of caps, knobs, or mounting rings in various devices.

In horology, 45 mm is a typical case diameter for larger wristwatches, particularly sport or premium models. The choice of this size balances readability, strap integration, and aesthetic proportion for many designs.

In optics and photography, some lens families use 45 mm as a thread or filter diameter. While not universal, it is among the sizes encountered in filter rings and accessory fittings.

In firearms and artillery, 45 mm denotes the bore and projectile diameter of a firearm. Calibers of this size have appeared in historical weapons in different countries.

Conversion notes: 1 inch equals 25.4 mm, so 45 mm is approximately 1.77 inches.