I recently purchased the 913D2 driver and viewed the SureFit assembly instructions via video as well as in print.  I changed my setting to D4 from the standard A1 setting.  When tightning the assembly screw it seems like I am required to exert quite a bit of force as i wait to hear the talked about "click" unlike in the video where it appears that a slight amount of effort accomplished the task.  The first time I attempted this I heard what sounded like a click but it also sounded like a noise made as the wrench bit slipped out of the screw.  I repeated the process, making sure that the assembly screw rotated freely as it began to tighten.  The shaft does appear to be firmly attached to the head so I assume everything is OK.