I have used all I need and have plenty extra. I bought these surplus so they are used but in great condition. Here are the specs: 316 SS, internal tapered 1/2" NPT threads on both ends, 3/4" straight external thread w/ locknut. I origanally bought new buna-n rubber o-rings as pictured but I don't like them. I bought silicone ones today and will be here by Monday. I'll include 1 silicone and 1 buna-n with each bulkhead and let you decide which to use. These things are very expensive new but I got a good deal on them and am gonna pass it on. I'm asking $12 each plus shipping. I think atleast five or six will fit in the $5 flat rate shipping box but I'll varify that tomorrow. As you can see in the pictures, some have a thicker nut but all function the same. Prosit!