Tube Fitting vs. Flare Fitting vs. Compression Fitting
1- NO

2- NO

3- YES!


Swagelok fittings are different than compression fittings and will not work. Both are very different than flare fittings, which have a tapered nut and require the tubing to be formed in a &quot;flared&quot; taper at the end (using a special tool) and do not use a sleeve (ferrule). They also use a different thread:

You may find that regular compression fittings are labeled &quot;tube&quot; fitting in your locale. Home Depot Canada has them, they include a brass insert (for plastic tubing) and ferrule (for all tubing applications; for your purpose do not use them.

Why don't you take your connectors down to the local mom &amp; pop plumbing / hardware shop instead of going to the &quot;big box&quot;, they likely have the part and will be full of good advice as well.
here's the link to the part at HD: 3/8 comp. x 3/4 mip adapter