Slack

"Slack" refers to the cumulative distance each car can roll before it transmits a force to the adjacent car. On each car there is some amount of free motion within the parts of the draft system, such as from the connection between the coupler and yoke, between the yoke and draft gear, or between the draft gear and draft stops. There is also some movement between the coupler body and the knuckle, although for modern designs of new couplers and knuckles the slack between the coupler body and knuckle has been minimized.