Draft Sill

The draft sill is the portion of the car's center sill that houses and carries the draft system. It is the main structural member through which a car's pulling and pushing forces pass, and it is found at each end of the underframe.

Where It Sits

The center sill is the central backbone of the car underframe, running its full length. The draft sill is the part of that backbone at each end where the coupling and draft equipment is mounted. It is often made as a separate piece, either fabricated or cast, and then joined to the rest of the center sill. Inside the draft sill sit the yoke, the draft gear or cushion unit, and the draft stops, with the coupler or drawbar extending from the end.

What It Does

When a car is pulled, draft loads from the coupler pass through the yoke and draft gear and into the draft sill; when a car is pushed or buffed, buff loads pass the same way. The draft sill carries these heavy in-line forces and feeds them into the center sill and the rest of the underframe, so that the whole train of cars can be pulled and pushed without tearing the ends off the cars. The draft stops in the sill are what actually transmit the coupler force into the structure.

Inspection

Cracks, breaks, and distortion in the draft sill are serious structural defects. Inspection criteria and condemnable conditions for the draft sill and center sill come from the AAR interchange rules and field manual.