For Bolt & Ejection Clearance
One piece rings and sub-base mounts scope to side of receiver, provides additional clearance for bolt handles, easier loading and ejection.
Big Book Catalog, Issue:66, Page:263
New Product Supplement, Issue:552, Page:009
SPECS: Rings: sub-base, aluminum, steel ring cap, black, anodized finish. Distance between rings - Long 3.7" (9.3cm), Short 1.8" (4.7cm).