The Iwata Airbrush Replacement Part I-725-1 PTFE Needle Packing is a little tricky to replace. It is in the front of the inside of the airbrush body. The needle slides through it and it provides a seal around the needle so that paint does not blow back into the airbrush body. The Iwata maintenance tool kit has a special tool for removing this part, or you can use a small screwdriver. It fits several Iwata models including the Iwata H-Line HP-CH, Iwata Revolution BCR Airbrush, Iwata Revolution CR, Iwata Eclipse HP-BS, Iwata Eclipse HP-CS, Iwata Eclipse HP-BCS and the Iwata Hi-Performance Plus HP-C Plus.