Type SP - Serrata Press Fit Drill Bushings

  Serrata Press Fit Drill Bushings are part serrated and known as
  SP Type Serrated Bushings. The SP Type drill bushing is similar
  to type P bushing but with a partially serrated OD. These bushings
  are designed to press into soft materials such as wood, plastics and
  soft metals. The top half of the bushing OD is serrated to prevent
  rotational movement and increased axial resistance in the jig or
  fixture. The second half of the Serrata press fit bushing is finish
  ground for accurate and easy location and positioning