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There were many brands offering hook-bead 27" rims, in both racing and touring widths, and both single- and double-walled styles.

These seemed to have been sold from about '75 to '89 as O.E.M. spec on road bikes.

The 27" Pasela tires in each of the three widths are among the widest 27" tires, almost fully up to their listed widths.
Only the Michelin gumwall (1-1/4" only) seems to measure as wide at 32mm (1.25") on a decently-wide rim.

Older 1" tires were the same width as 25c tires from the same period, up through the 1980's at least.

These 1" and 25c-labeled tires also carried molded-in designations of 20-630 and 20-622, respectively, during the later years of the 27" era.
The molded-in dimension was the more accurate.
I also bought "TurboSport" tires labeled as 27x1-1/4" which carried the (accurate) molded-in size designation of 26-622, made by Cheng/CST and sold by Specialized.

Current standard 1-1/4" gumwalls from Kenda, Cheng, etc. seem to measure 28mm wide on 22-23mm-wide rims after overnight inflation to rated psi.
But on the Varsity, with 28mm-wide steel rims, they measure 31mm after overnight inflation.

Performance sold 27x1" tires up until a couple of years ago that measured 21.5mm on 22mm-wide rims.

The IRC Triathlon was widely distributed in 27x1" width until recently, and was a very sporty tire with a tread thick enough to be called durable.

Current 27x1" Pasela tires measure about 26mm wide on a 22mm-wide rim, fully as wide as tires that some companies label 1-1/8"
Paselas in 1-1/8" size are easily as wide as most 1-1/4" tires from other brands, and I've had clearance issues after this full width took me by surprise.