Re: coupler size

The tender's coupler needed to have a larger capacity and not breaking under load as the entire train is pulled through it.

There are two important factors with couplers.

One is the mating surfaces. This standard has remained the same for decades and allows a contemporary locomotive to couple up to a hundred-year-old car.

The other has changed over the years. That is the mass of the coupler -- this is related to the pulling capacity of the coupler. Today the coupler shank and other dimensions are larger than the first automatic couplers. So the size of the coupler shank is increased, also the couplers are now much larger in a vertical direction and the mass of the metal behind the mating surfaces is larger.

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as Jim Grigsby wrote
Other styles of full size couplers in use on the S.V. include Janney, National, and Simplex. The outside dimensions of these vary considerably but they all mate perfictly. We even have two thoroughly modern shelf couplers, from a standard Ga. tank car, and they easily couple with the older types. They look rather strange in a narrow ga. consist however.

Brian Norden