Rationale: /91 application: "Not for Navy Use". Having a seamless construction wire>> /191 enables the improved configuration to be employed in thermocouple extension cables.>> The rationale has to do with the /91 being a tape-wrapped construction. As such it has forced hydrolysis test issues with inferior performance when compared to the seamless /191. Fluid susceptibility is of concern in Naval applications. That was the reason for the creation of /191, to address the issues. The /191 is simply an improved wire construction.