This is the smallest known size of cast metal type, measuring just 1/72 of an inch tall. It was created primarily as a technical showcase of a typefounder's skill rather than for practical reading, as it is nearly invisible to the naked eye. Handling and setting such tiny slivers of lead required extreme precision and specialized tweezers.
Heard on the job
The museum has a tiny display block set in American, and you actually need a magnifying glass to see the letterforms.