Tech Q&A: JIS vs. Philips Head Screws

JIS screws on a vintage Japanese bike carburetor.
JIS screws on a vintage Japanese bike carburetor. Note the small dot next to the cross slot.

Q: After owning Honda automobiles and Japanese motorcycles for years, I just found out about JIS. Can you explain what it is, and why nobody seems to know about it? To be clear, I’m talking about screws and screwdrivers that appear to be Phillips but are not. All of us who have ruined such “Phillips” screws can truly say, “It’s not my fault.”

Kevin Schilling, Ames, Iowa

A: JIS is the abbreviation for “Japanese Industrial Standards,” which is the government body responsible for homogenizing everything from bridge-building materials and techniques to medical equipment standards and testing. Even though JIS covers all aspects of Japan’s vast industrial endeavors–literally tens of thousands of specifications and rules–it’s one lowly screw-head standard that affects us motorcyclists.  

While the nuts and bolts on our Hondas, Yamahas, Suzukis and Kawasakis mate perfectly with metric wrenches, the JIS screw head, which resembles a Phillips head and was commonly found on the engine cases, carb float bowls, bodywork and other areas of older bikes, is in fact different and not particularly compatible with the traditional #2 Phillips screwdriver in your toolbox. 

JIS screws are denoted by a dot or a small “x” placed next to the cross slot. “They look similar,” says Jon Mullins, Race Support Manager at Motion Pro, “but the shape of the recess is different enough that the tools are not interchangeable.” Due to those different profiles, your trusty Phillips tip won’t fully seat into a JIS screw head, and may “cam out” as you attempt to loosen or tighten the fastener. The result is usually a stripped and mangled screw head, a rounded-off screwdriver and a frustrated mechanic.  

Factory trained mechanics and Japanese-bike aficionados are aware of the JIS cross-point driver, but the knowledge never seemed to trickle down to the DIY general public. Nowadays, hex-head fasteners have replaced JIS screws in most applications, but you’ll still find them on vintage bikes and the occasional modern machine. If you’re tired of butchering screws, you can always pick up the correct tool from Motion Pro. They offer a T-handle kit with #1, #2 and #3 JIS bits to tackle all the screws you’re likely to encounter. 

Source: RiderMagazine.com

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