Have you misread it? A 1:2.5 variation is utterly ridiculous.

No Keit, i did not misread.

Here is for nominal 0.25mm wire

Grade 1:

Overall diam min 0.267mm, overall diam max 0.281mm

conductor min 0.246mm, enamel min 0.021mm, enamel max 0.035mm,

conductor nom 0.25mm, enamel min 0.017mm, enamel max 0.031mm,

conductor max 0.254mm, enamel min 0.013mm, enamel max 0.027mm,

Actual enamel film thicknes min 6.5um, max 17.5um = 1 : 2.7 !!! = 12um +-5.5um !!!

Grade 2:

Overall diam min 0.282mm, max 0.297mm

conductor min 0.246mm, enamel min 0.036mm, enamel max 0.051mm,

conductor nom 0.25mm, enamel min 0.032mm, enamel max 0.047mm,

conductor max 0.254mm, enamel min 0.028mm, enamel max 0.043mm,

Actual enamal film thicknes min 14um, max 25.5um = 1 : 1.82 = 19.75um +-5.75um.

After all, if making the 0.25mm wire with an accuracy of +- 4um is considered good enough,

I do not thinck that a enamel thickness variation of max +- 5.5 or 5.75um is that unacceptable.

If it is, buffering with additional layer isolation helps.

Anyway, i circumvent all those uncertainies by just winding 2 layers and measure the static capacitance (the way i explained in #27 because it includes all the variables) and go from there.