US Patent 7621040 Optical selectable force impact tool

An user-friendly impact tool for wire end termination in which the pre-set compression of a main drive spring is adjusted by hand with an adjustment screw having a knurled knob that is both visible and hand-accessible through an opening in the housing wall, and also having a vernier scale formed partly on the outer housing wall surface and partly on the knurled knob itself to correctly indicate the pre-load adjustment position of the drive spring.