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We are talking about tapered ½" CGA (Compressed Gas Association) thread, similar to tapered NPT (National Pipe Thread in the US). Tapered tank threads usually use Teflon tape as a pipe-dope or lubricant not a sealant. US Divers (now Aqualung) introduced the ¾" straight NPT O-ring sealed straight thread in 1960, which is currently the standard in the US.