On the left is an older worn unknown brand AR15 extractor. Note the chips on the groove where it holds a case rim. The extractor spring has a blue insert. It’s replacement on the right has a black extractor insert, and an O-ring. The rifle the old extractor was pulled out of was having some extraction issues. The new extractor should put an end to those issues.
The M16 used a blue extractor insert and a 3 coil spring. Later a 4 coil spring and harder black insert was adopted. Sadly some companies have produced blue strength inserts in both blue and black. Bravo Company’s Paul Buffoni has said that the durometer measurement of the blue insert is 60, and 80 for the black insert. This shows that the black insert is harder.
Now there are 5 coil springs. When purchasing new extractor springs for a carbine, I would recommend buying the new 5 coil springs. The additional O-Rings and D-Fender rings are generally not necessary, but they can aid in extraction if you are having issues.