The pressure drops and heat transfer coefficients of helical vane inserts of four different pitch-tube diameter ratios were measured over a Reynolds number range of about 30,000 to 300,000. The heat transfer coefficients and the pressure drops increased with increasing mass flew rate and decreasing insert pitch-tube diameter ratio. A momentum analysis, based on solid body rotation, resulted in new expressions for the momentum and frictional pressure drops for fully-developed flow in these inserts. Helical vane friction factors and Stanton numbers, computed from the experimental data in accordance with parameters derived from the analysis, correlated with conventional plain tube expressions.