BMW  Crankshaft Harmonic Balancer Holder (E39/E46/E60/E61/E81/E83/E90/E91) - ZT-04A4041 - SMANN TOOLS.
Holds vibration damper when loosening and tightening center crankshaft bolt.
Application:
BMW E81 120d 163PS.
BMW E46 318d 116PS - 318td 115PS - 318dt 115PS - 318d 115PS - 320d 136PS - 320td 150PS - 320d 150PS.
BMW E90 318d 150PS - 320d 150PS - 320d 163PS.
BMW E91 318d 122PS - 320d 150PS - 320d 163PS.
BMW E39 520d 136PS.
BMW E60 520d 163PS - 520d 150PS.
BMW E61 520d 150PS - 520d 163PS.
BMW X3 E83 2.0d 150PS.

This tool is designed to hold the crankshaft pulley stationary while loosening or tightening the center (crankshaft) bolt. This is necessary to prevent damage to the vibration dampening element … the rubber ring that separates the outer and inner portions of the pulley.