I previously posted some questions but did not make myself clear. I am including photos of what my question was about.
There is a little irregularly shaped door on the face of the knuckle – I have only seen this feature on ATSF F-units and observation cars. This “little door” is a curiosity and I’m wondering if anyone knows its purpose. Thanks for your patience.
I don’t know for sure, but my guess would be that it has to do with the F-unit’s retractable couplers. Once the coupler is retracted, I would suppose there needs to be a way to unretract it again, and that door may be the mechanism that ultimately allows that to happen.
That is a type H ‘Titelok’ coupler, used to eliminate slack between couplers on passenger trains. The “door” has a rubber pad behind it for cushioning and to take up excess slack in worn couplers, if I remember correctly.