Thank you so much, Randy. Oldster has given me a good head start with his post, so thanks to you, too, Oldster

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My holsters are so tightly molded in horsehide, which is as thick and rigid as equal thickness Kydex after the former is hot-air dried, that I'm wanting to be clear what I might need to add to my 9mm blue gun (one of the few I acquired here in Australia because it is still their Armed Forces sidearm, and is marked Industria Argentina).
I'm comparing these dimensions:
View attachment 390790 the thicknesses at the sections circled A,B,C; and the dimensions D,E. I'm an expat and have learned to 'think' in both thousandths and in millimetres; and if I didn't my Vernier calipers do.
One of my holsters, an avenger style, for the HP, shows the relatively tight fit (nobody's getting a 1911 into this one without a mallet):
View attachment 390791