What is the ruling on agreeing to a percentage of thread waste in addition to the manufacturing wage?

There is no objection to manufacturing fabric and yarn for others for a known fee, as long as it does not involve aiding in what is forbidden. If both parties agree that the factory will deliver a smaller quantity of the raw material after manufacturing (for example, delivering 99 kg out of 100 kg of processed cotton) in exchange for the factory keeping the remaining quantity (1 kg) as compensation for potential waste during manufacturing, and the owner of the fabric agrees to this, then there is no objection to it. This extra kilogram becomes the property of the factory, and it may dispose of it by selling it or otherwise.