Manufacturer functional interchange
Toledo Gear TQ21 appears in the same manufacturer-published cross-reference row as Grove Gear BMQ821 at Match installed ratio · 2.06 in center distance.
Toledo Gear publishes TQ21 at 2.06 in center distance for c-face input / shaft output and lists the competitor models in the same TG-90 interchange row. Toledo describes TG-90 reducers as designed to be functionally interchangeable while requiring current rating and dimensional verification.
The manufacturer describes the target family as functionally interchangeable with the listed competitor model or configuration.
Grove Gear BMQ821 and Toledo Gear TQ21 are tied by the published source at Match installed ratio · 2.06 in center distance.
The source still requires ratings, dimensions, ratio, fit, and application conditions to be checked before ordering.