From this post links below, he did the "flame test" to them and concluded the black ADBV was nitrile.I went back and re-read entire thread saw no fire test done before my comment. Only saw Overkill comment saying, 'next up'. Nor did a read a fire test in initial ph7317 adbv thread.
https://bobistheoilguy.com/forums/threads/ph7317.349992/post-6001981
https://bobistheoilguy.com/forums/threads/ph7317.349992/post-6001998
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