Just a note to thank everyone that's expanded this entry.  I was the original creator of this entry, way back in 2004.  It was a stub to clarify "stressing" in a Railroad entry.  I was very green to the railway at the time so simply took what little information I could find from a Stressing Course handout.  (since moved away from PWAY/trackwork).  To clear trainwatchers query... In UK we use mechanical stressers/pullers (high tension pneumatics), on very rare occasions the rail may already be at neutral temperature when installing.