Friday Figures: Swords & Spells Stand Sizes

I got started in the hobby at the point where the only ruleset for mass D&D combat that I could find in stores was the last supplement for original D&D: Gygax's Swords & Spells (1976). Looking at page 2, I saw numbers for scales and recommend size for miniature figure bases. To wit:

Figure Mounting sizes from Swords & Spells

Those fractional values looked odd, but I never questioned them, assuming that the author had some deeper reason for them. But looking back more critically today: Why 5/8" (instead of say, 1/2")? Why 1-3/8", or 1-5/8"? Why so complex?

Now, consider the following. We'll take a few key measurements in millimeters, in multiples of 5, and convert them to inches -- in each case rounding to the nearest eighth of an inch. We get:

Conversions rounded to eighth of an inch

That is, (noting 6/8" = 3/4") we get exactly the figures on display in the Swords & Spells table.

It occurred to me to check this when looking at Chainmail (1971), which gives the option of using either 30mm or 40mm scale figures for man-size (or in the fantasy section for others races, corresponding options such as 10mm, 20mm, 25mm, etc.). It should also be noted that the base sizes shown in Swords & Spells, and even the Chainmail suggestions for 30mm-scale goblins, orcs, ogres, etc., closely matched those provided by the Warhammer Fantasy product all the way up to 2015!

Theory: Gygax had miniatures that were originally based in metric measurements, which he mechanically converted to imperial figures (to the nearest eighth-of-an-inch) for the Swords & Spells publication.