Lengths 6 and 8 inch with one or two slots. Each rail is also equipped with two rows of M3 taped holes.
You can mount screw type index stop bar using thous holes and possible double side dovetail .
I did make section of rail little different than usually and was able to engrave scale on each side of rail. Future preferred if rail is used as nodal slide. Rail is also equipped with front mounting hole (1/4-20 ) and dowel pin hole. This let you mount clamp on rail end. Very nice option when rail is used with lens bracket as lens support package .