Full length rail runs the entire spine of the MC51 all the way up to the front sight to provide 2 functions: (1) a large rail area for attachment of different accessories and (2) a rigid skeleton to add structural integrity and reducing flex. This set includes all required mounting brackets and screws, and even a custom front sight which replaces the old standard one.
Now that you have a longer scope rail, consider shopping for a scope in our ACCESSORIES - SCOPES section. If you choose high scope rings to elevate the scope, you can also opt for other low profile accessories to fit in the front portion of the rail (low so as not to obstruct the view of the scope). These could include an ICS laser battery box or other laser items. Flashlights might be too tall though.