The RigWheels RailDoll-2X adds a bottom wheel carriage to allow you to lock your camera onto rails. If you have a big investment riding on rails, it's great peace of mind to have a captive rail system. It is the perfect option for professionals who use large video/film cameras. The RailDolly has a larger footprint than some of the RigWheel's other options so it provides a bit more stability when using a full-size broadcast camera or similar. The RailDolly is also a good option for critical audio recording environments because operation is silent.
This configuration uses 2 RigPlates, four RigAxels and two different types of skate wheels. Another capability with the RailDolly is the ability to use it on square or rectangular rails. Square or rectangular rails can be much more rigid than tube/pipe so if you're going to be putting a BIG camera rig in motion this is an ideal option.