The present invention a bit holder for use with a drill chuck includes a shaft adapted at one end for releasably mounting to the drill chuck, and at the other end for releasably mounting tool bits therein; and, a housing connected operably to said shaft, said housing defining bit compartments for releasably receiving tool bits therein. The uppermost portions at both ends of the first device-isolation insulator film are located higher than the uppermost portions at both ends of the second device-isolation insulator film. When a memory block or sector is erased or programmed, the associated counter is set to a predetermined value while other counters are incremented or decremented. Between the filter bellows a flow space for the fluid is formed communicating with an end face of the main filter element, wherein each one of the filter bellows is embodied as a star-shaped filter with filter folds arranged in a star shape. A shell is provided to shield the insulating housing.