I have tried to search this in google but I haven't found a complete explanation, so I ask this here. I also have read other answers related with hex bit socket, but it still not satisfied.
How the mechanism in screwdriver hold the hex bit? The specific part that I'm asking is the groove area in the bottom part of this image:
I have screwdriver like in this image:
I noticed that the bits and the screwdriver bar (that have notches in its side) all have 1/4 inch size. Also, the screwdriver can hold the bit from the first image securely. And when I browse the cordless screwdriver and impact drivers, all have the same 1/4 inch hex chunk.
There is an article in Wikipedia about Hex shank, but it doesn't explain about the groove part of the bits, and what the history behind its design.
I'd like to know the mechanism inside the screwdriver to do this. I also want to know the history of why we stick with 1/4 inch size. While in the wrench, we had 1/4 inch, 3/8 inch, and 1/2 inch male square head: