Hello, I bought some DeWalt clamps. At that time Galaxus did not sell them. These clamps work well. The removable rubber often fell off so I glued it on. The disadvantage is that they are expensive.
If you're a do-it-yourselfer and have the time, you can probably make your own using a normal clamp.
Perhaps a generic product would do the job just as well.
The rectangular hole in the rail is 13.1x6.35mm And the rectangle of the clamp is 11.7x5.6mm. (A little too much play for my taste, but it's fine)