If you plan to use a filter wheel for imaging with a monochrome camera, it is important that you obtain the correct size filter for your setup. Filters usually come in 4 sizes; 1.25 inches, 31 mm, 36 mm and 2 inches. As a general rule, 4/3” format sensors or smaller can use 1.25” or 31mm filter sizes. APS-C sized filters use the 36mm filter size. Full frame sensors require the 2” filter size.
Like everything else in astro imaging, there is a formula to find the minimum acceptable filter size. The formula is:
S = sensor focal length
d = the distance between the filter and the sensor
f = telescope focal ratio
One additional thought; for wide angle lenses with very short focal lengths, you may be able to use a slightly smaller filter than is calculated.
Reference: The Deep Sky Imaging Primer 3rd Edition, Charles Bracken