International standards for reference connectors for medical devices. Basically, if you make syringes or IV lines with a screw fitting, the dimensions of that fitting need to be within some range so it'll make a secure connection to something else. Those are made out of plastic, all materials and dimensions are well defined for their usage and mass production, and have a decent tolerance to them.

But to check THAT tolerance, you have these metal screws that they need to securely attach or be unable to attach to. And since the metal fittings will be used for batch testing entire production runs of life or death parts for years to come, they go a little overboard with specifications.

I'm not sure if it really needed to be THAT precise, but that's just what it was