Yes, there is a short bolt to maintain the position of the plates together. These are turn plates, not slide plates. When positioning the car on this style of plate one needs to roll the car onto the plate.
a tip on rolling the car onto the plates, after a few attempts and having one tire or the other not centered on a plate. I was trying to set each plate an equal distance away from each tire then roll the car forward. I set each plate and pushed it firm against the tire tread. I then pushed the car back a half a foot to get room for a rolling start, then pushed the car forward and up on the plates. That centered the car to the plates pretty well.