I see a lot of posts referring to reasoning why phillip screws would not be used like how hard it would be to use nuts or the trouble of tapping, or that they would not look nice. I think those reasons are moot due to the evidence that when it came to props, especially light sabers used in the OT, they just did not care. These props were not made to last, just get through the movie or simply the scene. They probably had to build up a saber for Luke for ESB and the grips would not stay in place. A prop guy cut out some spots on the grip, drilled some tiny holes, and without any care whatsoever, pushed six sheet metal screws through the body.