I'm not remembering if the shackles on German Panzers were removable or not.
However, the use of a "C" hook affords speed in being able to hook up tow cables. I have a vague memory that the term-of-art is "towing link"--which likely has a simple handle in German like "Abschleppensteckerstucke" (joking, prerttty sure it's a "Anhängerkupplung" [ahn HAYn ger KOOp loohng] ).
Rather than have to grab wrenches and unbolt shackles on both tracks, you hook one C in, pass the eye to the tow cable on the other side of the C, and repeat at the other end.
For nautical types, particularly ancient ones like myself, a shackle is a connecting link, typically "U" shaped with the top closed by a removable pin. That pin is either threaded, or has a crass-fastener to hold it in place. A clevis is a shackle where the cross-pin does not extend past the bulk of the shackle. That allows a clevis to pass along a chain wildcat, or through similar fixtures. The closing link on a bicycle or motorcycle chain is a clevs, if not normally thought of as one.