The ARKEN OPTICS Rigid Precision cantilever style mount (20 MOA or 0 MOA) provides near 2.5 Inches of forward extension for better eye relief typically desired for use on AR style platforms. The Rigid Precision mounts are fully CNC machined from aircraft grade Aluminum resulting in the highest precision and tolerances possible. The optic manufacturer&';s specification shall always supersede Arken&';s Rigid Precision mount specification, unless higher. ARP-30 (20 MOA) Tube Size: 30mm Height: 1.5 inch ARP-34 (20 MOA) Tube Size: 34mm Height: 1.5 inch ARP-30Z (0 MOA) Tube Size: 30mm Height: 1.5 inch ARP-34Z (0 MOA) Tube Size: 34mm Height: 1.5 inch