20 moa Scope base (rail) 
recomended for hunting and long range 
Depending on your shooting needs ou may need 30moa in your rail for long range and extreme long range it is recommended. please select the correct fitting rail from the options below
for example for rimfire long range my recomendation would be a 30 moa.
for centerfire 20 moa is generally sufficient. 
for example shooting a 6.5 creedmoor at 1000 you would only need to dial somewhere around 8 MIL (or 27MOA) therefore even with scopes with as little as 26 MILs  with 0 MOA of inclanation in the rail would be fine for that distance.
Mind you with a 0 moa rail if you have an optic with 30MILS (or 103 MOA) of adjustment, you would only have 15 mils to adjust in the turrets, thus having a 30 moa rail (or 8.7 mils) would allow you to use a total of 23.6 MILS of the available internal adjustment. 
Keep in mid the stock picture in this add isnt exactly as your rail might look your rail will be specific for the rifle its designed for.
 
info from MDT:
DETAILS
MDT’s Scope Base Picatinny Rails are designed to make the mounting of your optics easier. They are machined from 6061-T6 aluminum, then hard-anodized black for a durable finish. The underside of the rails are profiled to allow the rail to be mounted flush on the receiver and to match the geometry of the ejection port. These rails are designed with a 20 MOA incline providing additional elevation adjustment from your scope*. A recoil lug has been integrated in the underside rail profile on models where the action’s design allows for this feature.
*Additional elevation adjustment will vary based on your scope specifications.
SPECIFICATIONS
MIL-STD-1913 & STANAG 4694 spec rails
CNC machined from 6061-T6 aircraft grade aluminum
Mil-Spec Type II hard anodized
20 MOA rail
Integrated recoil lug**
SA & LA options
Contoured for snag-free operation
HARDWARE INCLUDED
#6-48 TORX screws (rail base drilled to accommodate #8-40 screws also)