If the reference of your lens has never been equipped by Precisious, you must measure your lens.

How to measure your lens?

Use a Callipster:

Measure the diameter of the focus ring and its width.
Measure several times to be as accurate as possible.

Lens mod measure cine mod Lens measure cine mod Cine mod how to measure a lens

Use a paper ruler:

Download, print and cut the paper ruler (Becareful to print with the correct scale. Double check with a classic ruler.)
Measure the circumference of the focus ring and its width.
Measure several times to be as accurate as possible.