Woodruff key, 4x5mm.

1700-2000cc Type 4 engines - Crankshaft small pulley end.
1700-2000cc Type 4 engines - Alternator pulley.
T25 CU engine - Crankshaft small pulley end.
911 1978-1989 - Camshaft gear.
911 (964) 1989-1994 - Camshaft gear.
911 (993) 1994-1998 - Camshaft gear.
924/924S 1976-1988 - Camshaft gear.
944 1985-1991 - Camshaft gear.
968 1992-1995 - Camshaft gear.
928 1978-1986 - Fan viscous coupling.

Also used for the crankshaft pulley, camshaft timing gear and alternator of many other models.