Flat tenter lines stretch the extruded film prior to annealing or further heat processing.
From the en.wikipedia.org
Many of his fellow Republicans regard him as occupying the far-right fringe of the party, the ultimate small tenter.
From the washingtonpost.com
When the hoops have been driven home, the cask was said to have been gathered and the hoops were secured by a number of tenter hooks.
From the en.wikipedia.org
While the number of children working in spinning as tenters did decline, more were employed in weaving because weavers were expected to tenter extra looms.
From the en.wikipedia.org
More examples
A framework with hooks used for stretching and drying cloth
Fulling or tucking or walking ("waulking" in Scotland) is a step in woollen clothmaking which involves the cleansing of cloth (particularly wool) to eliminate oils, dirt, and other impurities, and making it thicker. The worker who does the job is a fuller, tucker, or walker. ...
(tentering) The stretching of cloth on tenters
(Tentering) Process of passing a wool fabric through the tenter.
Hook on which bleached material would be left to dry - hence, "Left on tenterhooks."
A person who stretched cloth on a machine while it dries.
A Fuller, who cleansed woollen cloth, or a person operating a machine or frame which used hooks (tenter hooks to be precise) in order to stretch cloth so that it dried even and square. The term can also be used to describe any factory worker who tended machinery.