Avocet TT30 clinchers were made in a 27 by 7/8 and were insanely light and fast rolling folding tyres that are also a little delicate... these are considered to be the best high performance tyre ever made for 27 inch wheels but they are no longer made and the last ones I ever saw were being sold at Harris Cyclery about 6 years ago.
They feel like tubulars on the road... the wheelset they lived on is now on my Garlatti and these are Araya 1W red label hoops of very good quality rolling some Conti 1000's.
I prefer using the ISO designations although I am fluent in French and fractional sizing.
In our collection of bikes I have 349, 406, 451, 520, 559, 571, 590, 597, 622, and 630 wheels and tyres... used to have a few 635 models too.
Back to the 630...
Schwinn and Raleigh both adopted this wheel sizes for a great number of their bicycles save for the top of the line racing models which often came fitted with tubulars and the Japanese also used this tyre size widely and as such, produced a good number of decent rims.
As such there are millions upon millions of bicycles that are still rolling around on these wheels and tyre manufacturers still produce tyres... this last little bike boom brought a lot of these bicycles out of deep storage and our sales of 27 inch tyres has been brisk for several years.