[Gnawrocki1]

Some seals that are used in the aircraft industry for the same purpose are known as Voi-Shan seals.  They are actually conical seals.

I ended up using them on a leaky joint that I could not fix by "tightening a little more" on the hydraulic slide.  I believe that the tube flare had some defect.  They come in all sizes for the "jic" 37 degree flare.

Here is a website for those who want to know more.  https://www.electronicfasteners.com/wp-c...lseals.pdf