单项选择题
A.密封管螺纹B.非密封管螺纹C.60°圆锥管螺纹D.英制螺纹
A.4NPSCB.4NPSC -LHC.4NPTD.4NPT -LH
A.RC/R2 1/2B.Rp/R2 1/2C.Rc/R1 1/2D.1/2NPT
A.防锈B.冷却C.清洗D.减震
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