WEAVER TOP MOUNT BASE NUMBER 13
USE AS FRONT BASE ON: MOSSBERG25, 26, 42, 46B, 140, 142, 146
USE AS REAR BASE ON: REMINGTON12A, 121 WITH 3/4″ BBLS, WINCHESTER 57, 69, 61 ROUND BBLS
http://www.weaveroptics.com/rings_bases/bases/top_mount_base_pairs/