Check out these interchangeable ornamental caps. The three ornamental cap blocks, in the center, have a square slot cut into them. This slot allows different letters of the alphabet to be exchanged when printing. The two letters (“A” & “N”), on the left and right, are printed examples of this. I scanned them from our original 1715 Apocrypha.
Printers in the 18th century often used these interchangeable ornamental caps, but not always. As an example of this, I have also posted a letter “A” that has been carved within its own decorative scenery and is not interchangeable.