CTC Replica Rear Chain / Sprocket Guard 
Yamaha Part Number 38V-22199-00, better known as a "Sharks Tooth" 
These have been made stronger than the original Yamaha part whilst maintaining a perfect fit.
These are fitted to the following Yamaha bikes
TY 250/350 Mono 1984 - 1992
TYZ 250 1992-1996
TTR125 / 225 2000-2004
XT225 1992-1997
XT600 1990-1995