A guide rail system is provided that allows multiple optical communications modules to be mounted in close proximity to one another on a host circuit board. A first portion of the guide rail system is secured to a bottom surface of the host circuit board at locations on the bottom surface of the circuit board adjacent an opening formed in the circuit board. A second portion of the guide rail system is disposed on bottom surfaces of the optical communications modules. The first portion includes one or more pairs of rails and the second portion includes one or more guide blocks configured to slidingly engage the rails. The opening formed in the circuit board allows the rails to be accessed and also allows heat from the module to be dissipated down into the first portion and then into a heat dissipation structure secured to the first portion.