I like hacksaw frames since, for such a simple design, various manufacturers have been able to apply surprisingly different innovations. This one is by the K-D Manufacturing Company of Lancaster, Pennsylvania. It accommodates different blade lengths by having notches in the top of the frame into which the top of a movable arm can lock.
Turning the knurled nut pushes the arm to the right, tightening up the saw blade in the frame. Finally, by pulling the lever at the right of the arm up and over centre, the arm is locked securely in place. It's an overly-complex design, but that adds to its appeal for me.
Two substantial steel pins on each arm allow for the saw blade to be mounted vertically or horizontally.
Two inventors, Harry W. Kulp and Martin C. Dellinger, founded K-D Manufacturing around 1920. The company ultimately specialized in automotive tools such as valve spring compressors. The company was eventually acquired by the Danaher Corporation which merged with Cooper Industries to form Apex Tools in 2010. In 2014, Apex rolled K-D into the GearWrench brand, and the K-D brand has all but vanished since then.