an extrusion die head for producing multiple layer tubular plastic bodies is disclosed in which the size of the tubular resin flow passage for at least one of the resin layers is infinitely adjustable at the point where two or more resin layers merge together to form a multiple layer stream . the adjustable passages are formed by two spaced inclined surfaces at the downstream end of the passages . the thickness of the passages is varied by axially moving one surface relative to the other . the moveable inclined surface is carried on an annular ring member mounted in the die head . in one embodiment , the ring is replaceable with another ring member to axially move the surface , thereby adjusting the layer thickness . in another embodiment , the ring member is threadably mounted in the die head so that rotation of the ring causes axial movement of the surface to adjust layer thickness . in the preferred embodiment the ring member is rotated by a drive mechanism operable from outside the die head for adjustment without disassembly of the die head . adjustability of the gap sizes in the die head widens the range the relative thicknesses of the layers and widens the range of relative viscosity values that can be used . the versatility and usefulness of the die head is thus increased over that of die heads employing fixed gaps .