I totally disagree with the pin striping dates...pin striping occurred long before the 1950's, in fact I have several cast iron book presses that date from mid-1800's that are pin striped, and several other cast iron items from the same era, also striped. Many 1900 to pre-1940's American and European cars were striped as well.
The hooks are certainly hand forged and I agree that they were visible ornamental hooks for a buggy, cart or springer.
The slot screw could date any time, in fact they are still made.
In addition, even hand wrought square nails can still be purchased today. I happen to have a box of nails in my woodshop.
Gypsy, good thought, however cross-tie hooks need to be strong enough (and much shorter and with lag bolts, not screws) to withstand a lounging horse, especially if it was plow stock, which is about double the weight of a carriage or HB stock.
When we didn't have a squeeze pen, we'd cross-tie bull stock for shots, ear tagging, and.....well, you get the drift.