The Hi-Hat Rails are designed to mount to the bottom shelf of both the Apollo 40 and 52 workstations. Installation is as easy as screwing in 6 bolts to the dedicated threaded holes located on the underside of the Apollo bottom shelf. The Hi-Hat board can be fed into the rails from both sides of the cart. Hi-Hat rails are compatible with standard 18 in. x 18 in. Hi-Hat boards.