A handle letter is used in tooling, both blind and gold, to impress a single letter in a design. The identical structure can also be used to impress a single ornament. In bookbinding, it is the more traditional alternative to type in a type holder.
====== <- brass letter or ornament
\ / can be any size
|| | brass shaft
|| | approximately
|| | 5 cm / 2 inches long
|| | 5 mm / 1/4 inch in diameter
| | \
| | |
| | | wooden handle
| | | approximately
| | | 10 cm / 4 1/2 inches long
| | | 15 mm / 1/2 inch in diameter
| | |
| | V
Handle letters generally come in sets of 39 - 45 pieces. This will comprise an entire font of uppercase letters in one size, plus numbers and some punctuation (at a minimum, the comma, period and ampersand).
Like all tools, handle letters are heated before being impressed in the leather (or other substance) to be tooled. Although the temperature required is very low (just enough to hiss in contact with water), most older sets show some evidence of scorching where the brass meets the wood. Bookbinders can be inattentive.
Titles tooled with handle letters are rarely perfectly straight. To determine whether a handle letter or a type holder with type was used on a given book, look for crooked letters and uneven impressions. These are not flaws in a fine binding, but rather the mark of hand crafting. Connoisseurs speak of bindings that have "a thousand minute fascets (sic), each with its own angle of reflection."1
1. Bookbinding for Bibliophiles, by Fletcher C. Battershall (1905)