Gibraltar Memory Lock SC-GCHKML

There are 2 versions of this clamp: with a wingnut or with a drum screw, like this one.
The wingnut version is easier to use because you don't need any drum key or whatsoever, but in reality this drum key version is a better choice.

Because a wingnut can get in the way in tight spots, and this version won't bother you with that problem.

The memo function is needed when you break down/ build up your set up regular, but it also functions as an extra security for a rack clamp with a heavy load.
The added advantage is that you don't have to tighten the main clamp like an ox, because now it has extra security.
Meaning your rack pipe takes far less risk to get dented as the weight on the clamp is now redistributed over a larger area (main clamp + memo clamp) of the rack tube.
For securing, you will need same brand memo clamps, because they're made for each other with special cut outs that fit into each other.

This is a hinged version, so it's possible to add them whenever you want without having to break it down first, like with the unhinged version.

But you'll pay for it. Gibraltar is not the only manufacturer that makes good, innovative stuff, but charges the customer dearly for it.