Fastener gripping apparatus can be used in connection with a shaft having a driver portion adapted to engage a bolt. The upper housing has a pair of integral pivot bosses that mount in horizontal pivot bores in the lower housing so the upper housing rocks between on and off positions. One end of an arm is associated with the sliding member, and the other end supports an umbrella canopy. Each twin-grating structure is selectively responsive to a unique wavelength of light to generate an optical interference fringe signal.