Cable Management Rail Kits are made of (12) pieces of 7 RMU sections of cable management "fingers." When used with ES enclosures, fingers are installed on the front of the rail using Great Lakes flexible mounting profile, a series of holes outside of the EIA pattern (used for fingers and other accessories). EN rails have more than one series of holes ( as pictures), so fingers can be installed on the front, side, or rear of rail. Fingers align with rack mount units on both enclosures, creating clean cable pathways. If used with E and ES enclosures, rails will need to be recessed 4.5"