Device on nose of tool that prevents tool from being activated unless it is in contact with the material. Automatic Tool is automatic. Just hold the trigger and the machine will continue to drive fasteners at speed set by the operator. Contact Trip Won't activate when trigger is pulled but will activate when trigger is pulled AND tool is tapped along the surface. Sequential Trip Won't activate unless tool is in contact with the material and the trigger is pulled. In that sequence. Usually, identified with a -2 or ST in the nomenclature Trigger Actuation Tool activates by simply pulling the trigger. No trip of any kind is on the tool. This trip is never used on more powerful tools like nailers, etc.