[ Primary Measurement ] The diameter of the mounting hole in the clock case is crucial. This correlates to the back side of the clock fit up which fits into the pre-drilled hole in a clock case. The mounting inside diameter is 1.50 inches (37.6mm). This increases slightly with the included ring gasket, ensuring a secure and snug fit. The mounting depth is 1/4 inch. [ Secondary Measurement ] The diameter of the visible part of the fitment (the clock face) is 1.77inches (45mm) . While this is an important measurement, some flexibility may exist in the diameter of the round clock insert depending on the clock case. . [ Long-lasting Battery ] Powered by a PC21 quartz movement with a long-life silver oxide battery (included), This quartz clock insert ensures reliable timekeeping for an extended period. [ Reliable and Silent ] This replacement clock insert offers accurate and dependable timekeeping, making it a practical choice for your home or office. It operates silently and accurately, making it an ideal choice for bedrooms, living rooms, or any area where a discreet timepiece is desired. [ Applications ] Round clock inserts are incredibly versatile, making them a great choice for a wide range of craft and DIY projects. They're designed to be easily integrated into various materials such as wood, metal, or ceramic. This adaptability allows you to create unique and functional mini clocks, whether you're working on a handmade gift, a custom-designed crystal clock insert, or a small-scale clock craft project.