Manufacturer functional interchange
Boston Gear 872B/873B appears in the same manufacturer-published cross-reference row as SEW-EURODRIVE R73 at Match installed ratio/application · Boston 800 size 870 · Foot mounted.
Boston Gear publishes 872B/873B for 800 Series size 870 in the foot mounted column of its in-line helical interchange guide. Boston states the 800 Series is designed to be functionally interchangeable with listed drives while requiring verification of ratings and dimensions.
The manufacturer describes the target family as functionally interchangeable with the listed competitor model or configuration.
SEW-EURODRIVE R73 and Boston Gear 872B/873B are tied by the published source at Match installed ratio/application · Boston 800 size 870 · Foot mounted.
The source still requires ratings, dimensions, ratio, fit, and application conditions to be checked before ordering.