[Dan McEachern]

Garden variety compression fittings on copper tubing tend to crack at the point where the ferrule bites into the tubing so they are not the best fitting for inside an engine where they are unaccessable. Generally flare fittings are a much better choice. Inverted flares are not the best, but where there is not much room to make a connection, they are still better than compression fittings. If you must use compression fittings, instrumentation fittings such as Parker, Gyrolok or Swagelok are preferable but are not inexpensive.