It is an integral-structured metal coupling with two spiral slits in the round material. It has a higher torsional rigidity compared with the HELI-CAL A model with single spiral slit. A perfect integral construction eliminates backlash. Maximum parallel offset 0.15mm and maximum angular misalignment 3deg. are allowed. The high-strength aluminum alloy material and alumite treated surface ensure a high-corrosion resistance. Two fastening methods can be selected, the set screw method ( DSR model) and clamp method ( DSCR model) . Normal torque 0.8Nm to 19.5Nm Drilled bores 4mm to 16mm Backlash Zero .