Nylon? - Cast, MD Filled is a dry lubricant-filled bearing material. Manufactured to be a more crystalline product with improved wear resistance, Nylon? - Cast, MD Filled also offers improved compressive strength. Cast Nylon MD tubes contains finely divided particles of molybdenum disulfide to enhance its load bearing capabilities while maintaining the impact resistance inherent to nylon. It is the most commonly used grade for gears, sheaves, sprockets and custom parts. Cast Nylon MD Tubes are Gray-Black in Color.