I bought this part not certain that it would fit my TTR125. There were apparently older models, pre-2006, with different exhaust diameters. When the part arrived, it bolted right on, no problems whatsoever. Now my bike is much quieter and the spark arrester allows it to be ridden on public trails. Without this insert, my bike was quite loud and I was hesitant to ride it at my friend's track or on the road (bike has a light kit and is street legal) and attract unwanted attention.