JIS vs ISO Thread Pitch
 

I searched this forum and didn't find a thread dedicated to describing the switch from the JIS to the ISO standard in 1967, so I thought I'd establish one. I apologize if this is duplicate information.

Many of you have already encountered this bit of information. I wasn't aware of this information before I started my project.

In 1967, Japan replaced the Japanese Industrial Standard (JIS) standard with the International Standards Organization (ISO) standard for its fasteners. In some cases, the thread pitch changed. This was most notable for screws in the 3mm, 4mm, 5mm and 12mm sizes. This is why some people have struggled with replacing the tank badge screws or have cross-threaded their petcock mounting threads when using new screws.

Here's an excerpt from a 1967 Honda technical service bulletin:

This change-over will be effective from the start of production of all new motorcycle models first produced after the beginning of 1967. In all other models, those previously in production, the change-over will be made gradually and on no set schedule

The full bulletin can be downloaded here.

The CA95 was built before the switch from JIS to ISO, so the thread pitch for 3mm, 4mm or 5mm screws will be different than the screws you'll find in a hardware store. I try to re-use fasteners whenever I can, but my bike was missing some fasteners, or in some cases, they were too corroded to reuse. For my CA95 petcock mount, I drilled out the 5mm threads and re-tapped the threads to standard 6mm ISO metric. In other cases, I found NOS replacement screws.

It's all simple stuff, really, but it just helps to be aware of the differences in the thread pitch for some of the old fasteners.

This screen grab from the Honda bulletin summarizes what we need to be aware of:

http://www.forths.com/blog/wp-conten...ISOpitches.jpg

Good info. My local fastener house said JIS what?

Done.

Hey,

Just found this....its the first kit I've found with the 3x0.6, 4x0.75, 5x0.9 taps and dies.

http://www.ebay.com.au/itm/221217950...84.m1497.l2649

Make my own missing bolts and nuts now...;)

Kev.:)

keep in mind that die-cut threads on a bolt are not as strong as rolled threads, so don't use hand-made fasteners for high-torque applications.

Yep, definitely will keep that in mind...;)

I'll probably just use them to chase and clean up ordinary and damaged threads.

Cheers,
Kev.:)

Thanks to this discussion, I just checked my $17 Harbor Freight metric tap and die set, and it has the old JIS thread taps and dies in it! I haven't had to use them, so their durability is yet to be determined.