JIS vs ISO Thread Pitch
Posted: Sat Sep 15, 2012 7:30 am
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.
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.
