Those fast hitch adapter arms look like the larger of the two sizes. They would fit the 300, 400 series and larger tractors made from 1955-mid 70s. There were dozens of models they fit, only identified as the larger size. Small fast hitch arms fit the Super C, 200,230 and small tractors.

Those are lift arms to convert an International tractor 2 point fast hitch to take 3 point hitch attachments.

References:

http://bid.hansenandyoung.com/view-auctions/catalog/id/5764/lot/650715/?url=%2F

http://i.ebayimg.com/00/s/Mzc1WDUwMA==/z/MR0AAMXQrhdTVjuA/$_3.JPG?set_id=2

Reason:
Definitely on the right track but I need to know which International they fit.

Those fast hitch adapter arms look like the larger of the two sizes. They would fit the 300, 400 series and larger tractors made from 1955-mid 70s. There were dozens of models they fit, only identified as the larger size. Small fast hitch arms fit the Super C, 200,230 and small tractors.

References:

http://www.antiquetractorsrus.com/internationatractorparts/hitches/Internatio...

http://www.robertstractor.com/Farmall-International-Tractor-Fast-Hitch-3-Poin...

http://www.farmcollector.com/implements/the-ih-fast-hitch-story.aspx