Product review (2 stars): This failure made me a pilot light expert !
Only worked for 3hr, then output died.  Used in 45yr old gas furnace.  Old gas valves need minimum 26mv output from thermocpl to keep pilot light on.  This White-Rodgers seemed weak from the start.  Probe is too slick & shiney to absorb pilot heat efficiently.  I bought another at Green Thumb Hardware, a Lasco part that looked like this White-Rodgers thermcpl.  Tested over gas stove, only read 25mv, didn't even bother to install that one.
Finally found perfect thermocouple at Lowe's, it puts out 27.4mv and works perfectly in my gas furnace. It's a Utilitech Water Heater Thermocouple, model 9008073046, Lowe's item # 362434, for $7.98.  The probe is dark & rough, and doesn't have shiney brass base at end of probe which takes up valuable space between the thermcpl holder & burner housing. It says "factory authorized part" on packaging, it's distributed by American Water Heater Co.  Looks much like the old thermcpl that worked in my furnace for more than 11 seasons of Ventura California winters.  Recommend skipping the hassle with this White-Rodgers universal part.