I have a question about the unit associated with the clearance in the diagram below.

As you can see, the measurements of certain parts of the Retaing Ring vary depending on the the variant (labelled PART NO) being manufactured  and certain measurements are hard coded. For example, the angle between Smax and Smin is hard coded at 135 degrees but so is the clearance at .004. The question is .004 of what? The diagram itself does not indicate and the two accompanying tables only frustrate the matter.

I'm tackling the MBU-50 variant and as you'll be able to tell, the clearance is barely visible. I converted the .004 inches into .102 millimeters, imagine if I had assumed the .004 was already in millimeters.

Can anyone definitively state what the unit associated with the .004 Clearance is and provide any supporting evidence so that I may be able to troubleshot a similar problem in the future.

Thank you in advance for your help and i look forward to hearing from you.