NMP stands for "no moving parts".  NMP blocks are designed for use in between the loop thimble and loop block. The fixed part is spliced through the central opening or suspended, and the block is secured through the milled slots by sewing or with a simple cable tie to prevent twisting. The loose part is between the jaws of the block.

NMP-D BLOCK TO BE MOUNTED ON DECK, IN THE MAST, ON A TRACK OR SLIDE
The NMP-D block is fixed by a stainless steel screw through the central hole; two smaller screws on the outer radius prevent the rope from falling off. Without these two, the block can be used as
a deflector, just flipping the line behind it.  The MWL mentioned is related to the block for horizontal force with its lower edge sunk into the deck. For different types of attachment and in relation to the stiffness of the deck or else, the MWL could be lower.

TyeTec NMP-Deck Blocks