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You may have heard the term "JIS" screw or screwdriver before - or maybe you have just wondered why your Phillips drivers stripped the screws on your Japanese motorbike/carbs/etc. so easily. Well, it turns out that the Japanese manufacturers actually don't use Phillips-head screws on their motorcycles; they instead conform to a Japanese Industrial Standard (B 1012), which involves a different driver bit.
That's the old JIS logo on the left and the new one on the right. You can identify a JIS screw head by the dot that is either pressed into or raised from the head, or sometimes an X - here's an example from a Honda CX650E accelerator pump screw:
So what's the difference in practical terms? Here's a diagram of the screw head differences:
The Phillips design is said to allow the driver to cam out - meaning that the driver will slip out of the screw head - once maximum torque is reached. I have not found anything in the patents to suggest whether or not that's the case - anyone with more info please let me know! The JIS head is supposedly not designed for this, however, and instead the driver strips the screw head. This issue is compounded by the fact that - or perhhaps it's the entire issue - the Phillips drivers don't seat as deeply into the JIS screw head as the JIS bits do. Here's the head of a #2 JIS driver:
We have reviewed a set of JIS impact drivers on this site - click here for the Megadora range review and pics.
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