2-Ear Pinch Clamp, Zinc Plated Steel, 0.669 - 0.787 Inch Clamping Range, 0.335 Inch Width

Nominal size on this clamp is 0.75 inches, and the actual clamping range runs from 0.669 to 0.787 inches. So as long as your hose outside diameter falls somewhere in that window once it's seated on the fitting, you're in good shape. If you're right at the edge of that range, size down rather than up. Oetiker's own installation guidance says if both ears close all the way flat, the clamp is probably too big and you should move to the next smaller size.

Go by the clamping range, not just the nominal size. This one clamps from 0.669 to 0.787 inch, with a nominal size of 0.75 inch, so it’s meant to land right in that neighborhood as long as your hose and fitting OD fall inside that range.

These clamps are designed to fit hoses with an outer diameter between 0.669 and 0.787 inches.