Rick -
I was able to find some information that may help here;
http://www.rotorclamp.com/design-eng-assist.php
# Hose Clamps
Rotor Clamp constant tension type hose clamps will compensate for changes in joint diameter due to compression set in a hose. This feature eliminates leaks and the need to re-torque a clamp. Factors to consider when sizing a clamp:
* CTB type clamps: The clamps have a number designation equivalent to the outside diameter of the joint to be clamped, expressed in millimeters (Ex.-CTB-27).
* HC (SAE Type "E"), HW and DW (SAE type CTW )- Clamps have a range of recommended application diameters, listed on the spec pages as "A, B and C" diameters. The nominal diameter of the clamp is the clamp size divided by 16.
* The joint diameter will equal the fitting outside diameter plus twice the wall thickness, including the tolerances associated with each.
* The clamp must be large enough to fit over the maximum diameter of the joint bead and hose at this point (see illustration).
You can use a smaller clamp on an application to increase force. This can be done by placing the clamp on the fitting, installing the hose and sliding the clamp "backwards" up to the bead. Ideally, a clamp should be sized to fit onto the joint when opened to 90% of full (as a safety factor) and close to no less than the nominal (size) diameter when in the final position.

- Nate