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-S BLOCK is used for the Mainsail Reef. Lowest weight in connection with an enormous MWL makes it the block for the job. The NMP-S block does have an additional slot for attachement flat on the sail. It will be attached with Dyneema® webbings to the sail and some handstitching through the outer slots will prevent it from turning. The webbings shouldn’t be sewn closer than 2 x B to the block to lower compression force.