I think you mean a flare nut wrench. It's designed to loosen the nuts holding brake, fuel and other restricted nuts without rounding them. Very useful tool. It looks similar to a box (closed) end wrench with a small cut-out in front to slip past the offending line. Usually six point gripping surface. Works like a charm.
Hope that helps.
Old trucks and old trailers . . . a comfortable combination!
A-6E All Weather Attack Driver, BUFF
USN Aircraft Maintenance Officer, Ret.
'91 Suburban R-2500 w/BBC
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