in my opinion, these clamp cauls are a necessity. they help to spread clamping pressure and thereby improve the effectiveness of the black clamps. be a little careful with the grooved ones. they can slightly scar some braces but that is the repairmans responsibility, not the clamping cauls responsibility.
The grooved cauls have helped me so many times by providing an even and steady connection with braces inside to allow good clamping pressure without slipping.
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