Hey guys,
I’ve contacted Mike from EZPZ some time ago regarding the Matsumoku tremolo arms and sent him something similar to this. He was very timely in his reply and also very appreciative of the information I sent him. Super-nice guy…
The original threads are an obsolete metric M5 x 0.90 diameter and thread pitch, known as Japanese Industrial Standard (JIS). JIS was intentionally and gradually phased-out beginning in the mid-60’s. The tremolo arm bushing that holds the tremolo arm is tapped as an M5 x 0.90. This obsolete JIS M5 x 0.90 metric threading does not play well with the standard 10-32 threads. One could attempt to re-tap the bushing to match the 10-32 threads of the replacement arm, but I don’t think there would be enough quality thread left inside the bushing to provide a robust connection. Furthermore, the tremolo arm bushing itself attaches to the tremolo fulcrum plate as a left-handed, M10 x 1.25. The M10 x 1.25 is a common metric thread, but the fact that it is left-hand and unique to this tremolo system alone would make one think a little more about doing any re-tap modifications.
The solution would be to begin threading your replacement tremolo arms as M5 x 0.90 thread and pitch because, although the obsolete JIS fasteners are no longer manufactured, the obsolete JIS taps and dies are still available from online tooling suppliers.
In about 1965 or thereabouts, the movement toward some standardization in metric fasteners was well under way, and the JIS** (Japanese Industrial Standards) people were beginning to align themselves with most of the rest of the world in making fasteners that would be interchangeable with the same thread specifications. The DIN*** standards seem to be the ones that were most favored and were adopted as the ISO* standards. As you mentioned, the main shift in the JIS screws was in the change from the previous JIS thread diameter and thread pitch to the now standard ISO specifications. This affected the smaller size fasteners the most, as far as the JIS screws were concerned. The more common sizes of 6 - 1.00, 8 - 1.25, and some others, were not affected.
Prior to 1967, the Japanese had a unique system of bolt threads, defined under a JIS (Japanese Industrial Standard) standard. Most of these bolts were the same as what we now know as a metric thread, but not all of them. In 1967 the Japanese adopted the ISO (International Standards Organization) standard for metric threads, changing the few sizes in their old standard that were different.
The change from JIS to ISO resulted in some differences to the bolt heads, but the most important change is that the thread pitches for some sizes of bolts changed as well.
Using a modern ISO metric fastener in place of a JIS fastener will probably cause issues including stripped threads and poorly fastened bits.
The Old JIS thread diameter of 3mm and pitch of 0.60 became the new ISO M3 x 0.50
The Old JIS thread diameter of 4mm and pitch of 0.75 became the new ISO M4 x 0.70
The Old JIS thread diameter of 5mm and pitch of 0.90 became the new ISO M5 x 0.80
The Old JIS thread diameter of 12mm and pitch of 1.50 became the new ISO M12 x 1.25
*The International System of Units (ISO) in 1960 is metric and was one of many attempts this century to standardize metric bolt sizes internationally. The ISO standards are widely used, and bolt diameters range from 2 to 20mm in three varieties of metric thread pitch: the standard, fine and extra fine varieties.
**There are still JIS fastener standards today; they are just slightly different than the obsolete standards of the 1960’s.
***A further standard, almost identical to JIS is the German DIN (Deutsches Institut für Normung - German Institute for Standardization).
Here is an awesome link to a Honda Bulletin from 1967 noting the changes.
http://www.drooartz.com/woad-local/medi" onclick="window.open(this.href);return false; ... hreads.pdf
Hope this clears some things up.
Mark
Just for grins... some original ends.
