Question On Size Designations For British Registered Envs

Having recently obtained a couple of British-style registered envelopes, made from cloth-lined paper and having a pre-printed indica to show payment of the registration fee, I find myself wondering about the letters used to designate the various sizes. These appear to be the official PO designations for the sizes:

F 5½" by 3¼"
G 6" by 3½"
H 8" by 6"
H2 9" by 4"
I 10" by 7"
K 11" by 6"

Can anyone shed light on the origin of these designations? I.e. are they an invention of the British PO or was there some existing envelope size standard that they adopted for these envelopes?

Perhaps the envelope sizes were related to paper/document sizes at the time?

Perhaps there will be a PENGUIN along soon to give a reasoned explanation?
In the meantime - will have some further info regarding registered envelopes.

Thanks!

I had actually found that site earlier today, it does seem to have a lot of good information on it.

Here is a scan of the nicer of the two registered envelopes that I mentioned in my first post:



This is a size "F" envelope. One can tell that it is from the first printing of envelopes overprinted for Togo from the date in the cancel. This first printing, which included 240 of these "F" envelopes, was in either very late 1915 or early 1916. The next printing that included them was in the Spring of 1918.

The London transit marking seems to be dated 5 August 1916. There are no markings on the reverse, apart from the crossed blue lines.

The book by James A. Mackay "Registered Mail of the British Isles" has 395 pages of closely packed information but I could find no reference to the origin of the size designations.

However, whilst browsing to see if I could find any references to those letters I was surprised to find that in the year ending 30th November 1882 some 5,441,464 envelopes were sold to the public.

The breakdown of those figures to the sizes was
F - 3,347,292.
G - 1,922,052.
H - 106,324.
I - 29,940.
K - 35,856.

I also tried a couple of web searches but no luck. - Good hunting!

Penguin thanks Scotzm for the plug (grin)

That was a neat cover from Togo.

Cheers
Ron.

I'm surprised by the numbers sold...that's a lot of Registered Mail.

The sizes were basically UK Post Office internal designations for various types of envelope or card, as far as I know -- the reason they start at "F" is that there were other types of postal stationery envelope (non-registered) that were designated A, B etc. The I size was little used and scrapped well before the end of the QV period, the H2 size for foolscap paper was dropped in 1940, and the rather small F size in 1966. (The K size was made smaller in 1967-8, but after complaints the original size was restored.)

Since many postal stationery issues for the colonies were organised from London, and used the same printers, they tended to follow the British sizes.