TS16949:2009, ISO9001:2000, DOT certificate Double layer nylon tube reinforced tube :1).Material: PA, Nylon ,Polyamide2).Size: O.D.× I.D. (mm)Wall thickness ... ) air brake coilsDouble tube--Trailer air brake reinforced hose, air brake coil with double layerDouble tubing--Double layer nylon tube,double braided tube,reinforced tube