The Zacuto Z-Rail Slide Mount attaches onto a Z-Rail to provide additional accessory support. A threaded 15mm rod port is located on the side, and a 1/4" thread surrounded by smaller threads are on top. Onto the smallest you can screw in a Z-Rail Coldshoe.
If you attach two Slide Mounts to a Z-Rail, you can connect a threaded Zacuto rod into each to create a dual rod setup, and onto this setup you can attach a follow focus and matte box.
The Z-Rail that the Slide Mount attaches to is 3 inches long, and the Slide Mount can be adjusted along the full 3 inches.