Absent any other data points in the instructions, I'd probably go with the 19mm callout since that figure is consistant between the text and the illustration.

An online converter shows that 19mm is just a tiny tad under 3/4".


Earl

__________________
Earl L. Cagle, Jr.
NAR# 29523
TRA# 962
SAM# 73
Owner/Producer
Point 39 Productions

Rocket-Brained Since 1970