its not an alignment hole, its a ball detent, its on the very bottom of the slide not the lower side, i do know about the half hole your talking about, and this isnt it.It is an alignment hole so you can take the slide stop off which in turn allows the slide to be removed. See page 37 of the 938 manual, the half hole on the slide lines up with a end of the slide stop which is underneath the slide. Kinda complex to describe it is a 1911 thing. If all fails google p938 diassembly and youtbe will have a video.