For loosening the timing belt by means of the water pump which acts as the belt tensioner.

46mm
1/2" Square drive

Access is impossible without this tool.

Models: Opel / Vauxhall - Astra F (1991-1997) / Calibra (1991-1997) / Carlton (1991-1994) / Frontera (1991-1995) 
                                                Omega (1991-1994) / Vectra (1991-1995) 

Engines: C18NZ / C20NE / C20NEF / C20NEJ 

OEM: KM409A