Coupler yokes serve the purpose of forming a pocket for the draft gear and maintaining the gear in proximity to the rear end of the coupler, so that forces applied to the coupler head are dampened by the gear. In standard freight car draft arrangements, a rectangularly shaped block of steel is interposed between the butt of the coupler shank and the front working-end of the draft gear. This block extends crosswise through the front end of the yoke gear pocket and is termed the front follower. The relative positions of the front follower and draft gear to the coupler butt are maintained due to the securement of the yoke to the coupler shank by a connecting key, or pin.
The yoke design is predicated on the draft gear and coupler shank end. The yoke draft gear pocket must be compatible, in length, to the gear length and travel afforded by the gear. The shape of the front end of the yoke must be suited to receive the butt end of the coupler shank with proper provision for the connection of these two items. Thus, different yokes are required to fit with each major design of coupler shank butt.
Coupler yokes are furnished in quenched and tempered Grade E steel. Front follower blocks are furnished in Grade E steel or an equivalent material. The Catalog Number suffix letter at the end of the Catalog Number indicates Grade E steel.
Grade E steel coupler yokes must be used with Grade E couplers.
The following AAR Specifications and Interchange Rules govern coupler yokes:
M-205 Design Test Requirements
M-201 General for Steel Castings
M-211 Purchase & Acceptance
M-212 Secondhand & Reconditioned
Rule 19 Yokes for Type E Couplers
Rule 20 Types E/F and F Coupler Yokes
Rule 21 Front Follower Blocks
Rule 90 Prohibited Coupler Yokes