The original header flange was way too thick to use the drz400 header bolts so I had to take the flange off of the stock pipe and slightly modify it to be used with the new header. Was a little hard to get it to bolt up to a Yoshi slip-on too but I was expecting that. Overall it's a great mod for the price, I could feel the bike gained some mid range and top end power.
had to replace stock header on my 06 crf250x, I was a little concerned about it fitting as my local dealer told me it probably wouldn't. I phoned Dennis Kirk and they confirmed with their tech that it would fit and when it came I had no problems installing. I also saved a reasonable amount of money buying thru Dennis Kirk , which was key in making the purchase in the first place.