Speaking of unusual lead numbers —
When I first saw one like the Ruwe Hospital 4/8, I thought it actually had an extra-soft lead. A quick test proved that it didn’t. Obviously (in retrospect), a leading “2” was intentionally omitted on these pencils. This was apparently done so that the numbers in the fractions could be large and oriented in the same direction as was used for the 1, 2, etc. hardnesses.
But even when the style of the Blue Band changed and truncation of the numbers was no longer appropriate, it was initially retained —
In an earlier post, I showed that pencil companies have distinctive ways of expressing a 2½ lead hardness. They also have come up with unusual hardnesses and corresponding lead numbers —
The Templar’s 1-5/8 is “Exclusive with Reliance” —
Theoretically, that would be just a tad harder than the Berol Mirado’s 1½.
In fact, Eagle (the forerunner of Berol) had a 1½ , and also a 3½, back in the 1800’s —
The Eagle card also provides details of an old B/H system that was used for high-quality art and drafting pencils. They squeezed an FHB between HB and F.
F is not an unusual grade, even for regular pencils, but only Eberhard Faber put it equal to 2-3/8, as far as I know. According to this Berol Black Warrior, F (literally, F2½) is equal to 2½:
American pencils intended mainly for writing (as opposed to drafting) often come in a range of grades, with 1 as the softest and 4 as the hardest. But who actually uses the 4’s for writing? You’d have to be quite heavy-handed, or perhaps trying to write secret messages. They are relatively rare.