Pipe for the 2003 ktm 125 sx,The best,Pipe for that bike would be a Pro-Curciut Exaust system.Get the platuim pipe or the factory pipe,there both exactly the same deminsions,An get a Pro-Curcuit 304 factory Shorty silencer,with the pipe.That FMF exaust Does,ent give you as much a performance gain as the Pro-Curcuit does.Pro-Curcuit gives you alot more low end an mid an top end,plus all the over-rev you want,Pro-Curcuit is 100% deducated to providing big horsepower gains,an that is axactly what you get from them,an awsome performance shop,They have there own mx team that races the pro,s every race,An get this,there bikes are made up of the same parts you can by,They run the same exaust you can by,Plus they when an beat the factories all the time,they won the 2004 ama supercross series.You can never go wrong with them.