Hair Trigger
Source
Hair Trigger sold by many engineering suppliers in Northrend.
They can also be "skinned" by engineers from corpses of mechanicals in Northrend.
As an ingredient
Engineering
Patch changes
Patch 6.0.2 (2014-10-14): Stacks to 200, up from 10.
Patch 3.0.2 (2008-10-14): Added.