As Gagaryn said , a flooring cramp. When laying tongue & grooved flooring in order to tighten the joints.
The first couple of boards are laid and fixed close to the wall, thereafter 6/7 boards are laid, the ends are levered closed and the cramps are applied to the free edge of the boards with a piece of scrap where the cramp is to be used. The toothed cams sit astride the joist and grip as the ‘T’ bar is turned, the front section moves forward
Compressing the boards ready for nailing.The process is repeated until the floor is finished.
The cams accommodate from 40 - 100 m