Im guessing you screw the male end into your test pipe and then the o2 sensor iinto the female end. Included is three different sized jets. Is it just trial and error to see which one works with your car? There's a small, medium and large hole for the jets. Then there is like a black washer, but it's not completly round. Theres two little holes like you put those pliers on it and it spreads it apart. Sorry about this I dont know what its called. Does any one have any info or pics that could help me out with this?