polyamide plastic fuel lines which are dimensionally stable and resistant to fuels , alcoholic fuels and alcohols as fuels are prepared from aliphatic high molecular weight polyamides . the fuel lines are prepared by extruding a hot melt of the polyamide , sizing through a die having a diameter in excess of the given diameter of the fuel line , cooling the fuel line in a cooling bath , removing the fuel line from the bath and sizing the fuel line adiabatically through a disk having a diameter less than the given diameter .