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Japanese Fasteners

If there’s one thing working on Japanese cars (like my 2007 Mazda MX-5 Miata) and motorcycles (currently a Kawasaki EX300 Ninja), it’s that not all fasteners are created equal. Even metric fasteners. The metric world is torn between DIN (Deutsche Industrie Norm – German) and JIS (Japanese Industry Standard). Insert reference to Axis powers.

Let’s start with the cross-point fastener. In the US, we call these Phillips head screws, but there are some differences:

The difference is subtle, but important. The JIS bit actually digs in when trying to loosen or tighten. The Phillips head is designed to “cam out” and avoid too much torque. This can be very annoying when loosening a stuck fastener. While they look similar, note how rounded the root is on the Phillips driver. To make matters worse, this root prevents the bit from fully engaging the slots in a JIS fastener, increasing the chances of damaging the fastener.

Well, okay, Phillips head isn’t strictly German, or even metric, but you get the idea – the Japanese do things a little differently.

More to the point is the difference in bolt head sizes used for JIS and DIN metric screws and bolts:

Now, here’s the problem. M8 size bolts are pretty common, but notice the head sizes start to differ between DIN and JIS. Most inexpensive tool sets (socket or wrench) will include 13mm, but not 12mm! Sure, there are exceptions, but by and large, you have to double check that the set includes 12mm. This might be acceptable for a cheap Harbor Freight toolset, but my handy vintage (back when they were good tools) Sears Craftsman sets also miss 12mm. Strangely, they give me 15mm (which isn’t used, at least for bolts), but they miss good old 12mm.

So lesson to learn here is to ensure the tools you have are appropriate for the job your going to do. Don’t try a  Phillips head screwdriver on your Japanese car or motorcycle, and make sure you’ve got 12mm sockets and wrenches in your toolbox.

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