Böllhoff repair kit HELICOIL ® Threaded inserts for metal, stainless steel. Spark plug threads to DIN 72 502 Content: threaded inserts, combi taps, installation mandrel. Dimension: M14 x 1.25 Contents: 10 Appearances in lengths of 8,4 - 12.4 to 16.4 HELICOIL ® plus thread inserts are made of austenitic chromium-nickel steel (tensile strength of at least 1400 N/mm2). The rolled screw thread has a high surface quality. This ensures a high-strength, wear-resistant thread with an extremely low and constant thread friction. With repeated screwing a higher and constant biasing force is thus obtained for the same torque. This also leads to a better utilization of the yield strength of high-strength bolts. Significantly reduces the torsional stress is: compared to cut threads, the surface roughness is lower HELICOIL ® plus up to 90 percent.