Looks like older tent tensioners.
New ones look alot like what DC Matt has shown, but older ones meant for proper expedition tents or military tents where often very heavy duty.
My X-Gear (Tent and Chow Hall) are from a new firm called Robins and the use these on the Prospector series and large Cabin tents. I have the 24 person that fits 12 disco bunks, but my line tensioners are only like 40mm long.