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721 cross-reference: S921, S200, 20S, M21 | Replacement Intelligence

Manufacturer-published cross-reference

721

Boston Gear SMR cross-table row · Match installed ratio (5:1–100:1) · AGMA unit size 2.06 in center distance

PublisherBoston GearCheckedSep 21, 2026

Claim typePublished manufacturer cross-referenceRatioMatch installed ratio (5:1–100:1)AGMA unit size2.06 in center distanceOpen source table ↗

Models printed in this source row15

Publisher targetBoston Gear721

Published comparisonBaldorS921

Published comparisonDodge TigearS200

Published comparisonDodge Tigear-220S

Published comparisonElectraM21

Published comparisonFalk Omnibox1206WB

Published comparisonGrove GearB220

Published comparisonHub City211

Published comparisonLeeson 600 SeriesB621

Published comparisonLeeson 800 SeriesB821

Published comparisonMorse Cobra21U

Published comparisonMorse Invader721B

Published comparisonMorse RaiderU206

Published comparisonOhio GearB2206

Published comparisonWinsmith920DN

What the evidence supportsClaim scope

Boston Gear P-8565-BG publishes 721 as the 700 Series dimensional-interchange target for solid output shaft — non-flanged reducer (basic unit) at 2.06 in center distance. The table establishes dimensional interchange; gear ratio and application rating must be matched separately.

This page does say

These model numbers appear together in the cited manufacturer-published cross-reference row.
Boston Gear identifies 721 as the target model in that published row.
The source associates the row with Match installed ratio (5:1–100:1) and AGMA unit size 2.06 in center distance.

This page does not say

Every competitor model listed beside each other is independently certified as pairwise interchangeable.
Every installed accessory, bushing, motor mount, backstop, shaft, or screw-conveyor component will transfer unchanged.
The cross-reference removes the need to verify application torque, mounting, environment, and configuration.

Before treating it as a drop-in replacementVerification checklist

Ratio & speedVerify the actual ratio and required output speed.

Bushing / boreConfirm the installed shaft diameter and the required tapered bushing or bore arrangement.

AccessoriesCheck torque arm, backstop, motor mount, belt guard, screw-conveyor flange and drive shaft individually.

Torque & serviceConfirm continuous/peak torque, service factor, starts, shock load and thermal duty.

EnvelopeVerify center height, housing clearance and all mounting dimensions against the drawing.

EnvironmentConfirm lubricant, seals, ambient temperature, washdown/corrosion and hazardous-area requirements.

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