Use these nuts with quick-assembly brass compression fittings to create a seal on plastic tubing. They have a built-in sleeve (ferrule), so the sleeve is positioned correctly for installation. Thread the nut onto the fitting, then insert the tubing and tighten the nut. They have good corrosion resistance.Brass sleeves have better durability than plastic sleeves. Acetal sleeves are softer than brass, so they won’t damage your tubing.block 97>