Being simple plastic you’ll be fine. Obviously clamping it really really tight like its on a battleship would be silly, but tight enough so it doesn’t move wont be any problem.
Pace carbon forks has removable clamps on the legs for canti studs., and while they were the correct diameter, it still required quite a lot of clamping force to stop them moving in use. Securing a simple bracket for a guard will be nowhere near the torque you put on those.
Shown here. Now you can imagine something that holds a brake on it would be pretty damn tight.
*** Can I ask what guard it is ?. Im in the market for something like that myself.
Consider protecting the fork leg with tape. Any grit in there with a vibrating movable bracket and you’ll be into the CF.
You can get zip-tie/strappy-type bottle cage mounts that might be friendlier. Consider double-sided tape to hold any bracket more securely with a lower clamping force
Thanks @dyna-ti that does make me feel much better actually. As for the guard, it’s a Cube Acid 65 I have laying around — there are probably nicer and more readilly available things from SKS to look out for though (Velo 65 and Blumels 75 for two)
And yes @timba I’m an obsessive taper so will def do that. I hadn’t thought of using double-sided tape though, that’s a good call
You’re worrying about nothing really because those clamps put barely any stress on a fork – if you’re still concerned, fit them as the bottom of the fork by the drop out as they are pretty well solid material due to the way they’re made. The fork crown is also probably alloy so no worries there either. Main concern is cosmetic damage due to tiny grit particles getting between the clamp and the clear coat- put some tape over the clamped areas first.
You’ll be fine. Top tip, the cateye light seatpost clamps with a rubber insert make for good attachment points for typical round profiles. I use two to secure a rack to my recumbent trike.