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Mikuni "JIS" #2 Carburetor Screwdriver


JIS-Spec cross-point screws are generally marked with a single Dimple. JIS Screw Drivers always fit Phillip fasteners, but Phillips drivers may not fit JIS fasteners due to the slight design difference. Anyone that has experience loosening or tightening the Mikuni soft screw of “C5=0414-K”, knows about this issue. If you use the standard #2 Phillips screwdriver on this screw, you can easily strip the screw.

A JIS and a Phillips® screw may look the same to the human eye, but they have completely different profiles and it is important to know the difference. Henry Phillips invented and patented the Phillips® design in 1936. The Phillips® design was a great solution for the automobile production lines since it was designed to “cam-out” after a certain torque was reached to prevent over-tightening of the screw. Another advantage over the use of flat head screws was that the Phillips® self-centering design allowed operators to engage the tip of the driver into the screw head very quickly and easily. Japanese engineers developed their own cross-point design similar to that of the Phillips®. The Japanese cross-point drivers also have the self-centering and quick tool and screw engagement, however, the “JIS” (Japanese Industrial Standard) design allowed torque and over-tightening to be controlled by the operator and not at the head of the screw. This key difference is why Phillips screwdrivers cannot properly engage "JIS” (Japanese Industrial Standard) screws.

It’s very hard to distinguish the difference between a Phillips® versus a JIS screw without magnification. Some JIS screws can be easily identified by a single dot or dimple on the head of the screw. However, it could be difficult to identify one from the other if the screw doesn’t have a marking.