This is a stop for the Festool MFT/3 rail guide.
It has a foldable steel bar so that multiple stops can be set up and used on the same rail.

The block is assembled with two M6x20 bolts, two M6 nuts and a washer.
The knob was designed with the great nut knob generator: http://www.thingiverse.com/thing:713300, and thus requires that one of the bolts has an hex head.

It is preferrable to use a locknut (with a nylon insert) to secure the steel bar or it will get loose as you fold/unfold it.
Also, an additionnal nut can be added just under the knob. It will help releasing the block in case the underside nut does not go down by itself. This requires a longer M6x25 bolt.

I did not try to 3D print the steel stop as I thought it would be too flexible at the original thickness. Instead I cut it with a metal saw in an old shutter hinge. I also used files and sandpaper (and time and sweat) to get it to the final dimensions.