One camera store I visited occasionally in the 60s had a "crop Mat" provided by their photofinisher on the counter. you could send in a negative for printing and specify the desired Crop number.
When the lab I once used stopped processing film they gave me all of their crop cards, but when I asked for the crop mat they told me it was already gone. Those were really handy when not carding negs yourself. Great visualization tool within the given constraints.
One email just sent at 11:15pm PDT with Front scans of cards. A PDF describes the dimensions of the cards.
A second email was set a few minutes later with Back scans of cards.