15 30 2 30 20 20 30 3 15 15 30 4 30 20 20 30______________________________________ the testing method used to measure the frictional resistance between the metallic sheath having the inner peripheral surface coated with the solid lubricating coating having the aforementioned composition of components and the tendon inserted into said metallic sheath and the results thereby obtained will now be described 1 a spiral sheath kogen kizai name of goods having an inside diameter of 35 mm and a wall thickness 0 23 mm was used as the metallic sheat and a solid lubricating coating of 20 microns thickness having the composition of components in said example i 1 example ii 1 example ii 4 example iii 1 example iii 3 example iv 1 and example iv 4 was applied to the inner peripheral surface of said metallic sheath 2 a tendon twisted wire consisting of 19 wires having a diameter 21 8 mm was used as the tendon a testing apparatus as shown in the single figure was used to conduct the testing method a sheath 1 of length 10 cm was prepared and divided into two sections in a longitudinal direction which were arranged in steel mold frames 2 2 respectively thereafter concrete.