I use MK Aluminium Profiles made in Germany and the inside track is square. So some of the t-nuts here wouldn't work. Also I wanted something that self centers when tightening and can be inserted even if the ends of the profile are closed up.

The "T-Nuts" use regular M4 & M5 nuts pressed in and are 10mm wide. The angles are at 45 degrees which means that as you tighten it its pushes against the sides forcing the screw in the middle of the opening.