I purchased this XR/CRF-50 stock carburetor main jet kit to get my 2003 Honda XR-50R carburetor jetted correctly. I replaced the air-filter system with a UNI - 2 Stage Clamp-On Foam Air Filter & replaced the exhaust system & needed just one size larger main jet & used the #59 main jet to get it running right. The main jets are Chinese made & not OEM Keihin carburetor jets, but I had no problem with them in any kind of way & they are made out of good quality brass. If I had to make one complaint it would be that there should also be a larger main jet kit available with main jets like sizes #62, #65, #68, #72, #75, & #80 for those who need larger main jets to run the stock carburetor with a 88cc big-bore kit. These are good quality main jets & I recommend them to anyone who needs to tune there stock carburetor correctly.