The United States never did switch over to the metric system, as it was planned in the 1960’s and 1970’s. Yes, metric went over like a lead balloon. Americans are happy with inches, feet, gallons, and yards. The centimeter, liter and meter were mostly rejected. Both systems are used today in 2021 in labeling food products and liquids, but we Americans have learned to skim over those parts of the label that don’t fit into our familiar system.
The scientific community is firmly based on the MKS and CGS systems (meter, kilogram, second) and (centimeter, gram, second). The biggest part of the world is metric-based also.
Fortunately, pipe diameter tape measures are made for both systems, separately, and there is even one that is made with the inch and metric system together. The front side of the tape is in diameter inches (up to 38). The back side is in diameter millimeters (up to 955). This is a rare tool, but some companies need both measurements to satisfy their requirements.
Pi-Cobra Diameter Tape, Metric & Inch