The geometry of the area the bit slots into is different
I believe the difference is that the Philips bit is kind of a star shape, where the blades and the slots that fit together are widest at the middle where they converge, and narrow towards the outside, creating a wedge that ramps the bit out of the fastner. And with JIS they don’t narrow, creating a simpler plus shape that functions like two flatheads intersecting with eachother, but with a pointed tip so its self centering
The dot is there to communicate which kind it is since they look a lot like Philips. I believe thats also why posidrive has the little lines- so you can tell the difference. No idea what posidrive is about, maybe its similar 🤷🏻♂️
Edit, I was able to find some diagrams attempting to show the geometry differences (sorry, the side depicting each geometry swaps between the two pictures)
Note that according to hardware manufacturer Tekton, the differences are smaller than you think and especially the diagrams are highly misleading as they actually compare PH2 and PH0.
Just about the only major difference is the thread pitch and that is only different in JIS screws if they don’t have the dot.
The geometry of the area the bit slots into is different
I believe the difference is that the Philips bit is kind of a star shape, where the blades and the slots that fit together are widest at the middle where they converge, and narrow towards the outside, creating a wedge that ramps the bit out of the fastner. And with JIS they don’t narrow, creating a simpler plus shape that functions like two flatheads intersecting with eachother, but with a pointed tip so its self centering
The dot is there to communicate which kind it is since they look a lot like Philips. I believe thats also why posidrive has the little lines- so you can tell the difference. No idea what posidrive is about, maybe its similar 🤷🏻♂️
Edit, I was able to find some diagrams attempting to show the geometry differences (sorry, the side depicting each geometry swaps between the two pictures)
Note that according to hardware manufacturer Tekton, the differences are smaller than you think and especially the diagrams are highly misleading as they actually compare PH2 and PH0.
Just about the only major difference is the thread pitch and that is only different in JIS screws if they don’t have the dot.
I appreciate it. That was what I suspected, but it’s so hard to tell from just a picture.