Depending on what fitting you are referring to, a flare fitting, inverted flare fitting, compression fitting, or a fitting that relies on an O-ring needs no sealer on the threads because the threads are not the sealing surface. Pipe threads typically call for sealer, brass to brass or brass to steel may not need sealer due to the soft nature of the brass allowing the threads to conform to each other.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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