Firesleeve Clamp, 3 dia x 3/8 wide

It's made for a 3-inch diameter hose.

That's exactly what it's sized for. The FF9217-0648S is a 3-inch diameter clamp, so it pairs with 3-inch firesleeve. The clamp itself is 3/8 inch wide, which gives you a clean, secure hold without taking up much real estate along the sleeve. It's an Aeroquip-manufactured part under the Eaton/Danfoss line, so you're getting a purpose-built fit rather than a generic band.

Fit comes down to the clamp diameter and width. This one is a 3 inch diameter firesleeve clamp that is 3/8 inch wide, so it matches a 3 inch firesleeve size requirement.

This clamp is designed to fit a 3-inch diameter hose. It's also 3/8 inches wide.