what thread type for gas tight threads?

[BrokenBiker]

This is why I love this forum, so much knowledge

 

[addjunkie]

Taper to taper joints should in theory self seal, the ptfe tape is to let the threads slide past each other until it is tight enough to seal.

Problem is that the threads and tapers on mass produced fittings are less than perfect so you will never get them tight enough to self seal.

Stainless fittings will gall long before they are tight if you don't use a liquid sealant.

If you want to get an elbow or tee to point a certain direction once assembled that might not be the same position where the joint is tight. That's where a solid setting liquid sealant is essential to hold the joint in the right position.

Id suggest Loctite 571 and taper to taper fittings. Its only low pressure, the OP planning on using. If it were high pressure I go 10k fittings in Stainless, NPT or BSPT. If you want high pressure reusable fittings look at JiC.

Ive used the Loctite 571 successfully upto 400 bar gas with out issue.