Lunging Attachment

They don't make them anymore! Ugh!

These are probably the most similar:

Lungeing Attachment | Dover Saddlery

Tough-1 Lunge Line Connector | Horse Tack Online

Tory Leather Lunging Attachment - HorseTackCo.com

Featuring:

"Tinka Van De Weideweg"

24 years young, 14.2hh, Palomino colored, Imported from Holland and Registered American Haflinger mare (NL HFL 21334)

Registration number: 11968-98

Sire: "Angelo" (NL Hf.K.134)

Dam: "Alize Van De Haflinger Hoeve" (NL Hf.K.4934