Do not select by diameter alone
Study the bell together with its support and striking mechanism. Record outside diameter, height, opening and fixing details, with photographs showing a clear scale. Measurements embedded in an old address may be poorly transcribed. Confirm every value and unit instead of treating the previous title as a specification.
Describe condition and limits
Ask about cracks, chips, deformation and known intervention. A sound recording depends on mounting and recording conditions; it does not prove that the bell will suit your movement. Patina or a similar shape is also insufficient to establish that two components originally belonged together.
Give the clockmaker a complete reference
Photograph the existing support, hammer, available space and remaining parts. Send these images with the proposed bell measurements to the professional responsible for the work. Do not modify holes or supports before the approach is agreed. Retain before-and-after photographs and describe any adaptation clearly in the clock’s record, rather than presenting it as an original configuration.
For the next part of your selection, read Antique French mantel clocks: case, movement and placement.