There is one H Block that is threaded and one that is not. The non-threaded block is designed this way to prevent the screw rod from jamming when it is turned. If both blocks were threaded, it could cause issues. The non-threaded block allows the screw rod to be tightened while pressing down on the H Block and compressing the spring, enabling it to automatically adjust its position as needed.
The bottom H Block is threaded because it serves as the mechanism for compressing the screw rod.




