Identifying a JIS headset

Todd Bryan said:

Greetings to all. The original headset on my circa 1979 Miyata "Seven
Ten" frame is indexed and I want to replace it. I don't know if this
headset is ISO or JIS, and I'd rather avoid pulling the fork and races
to measure it. Are there other telltale identifying signs to look for?
The headset is unmarked, but it does have an odd 33 mm lockring.

That is almost certainly J.I.S.

Sheldon "Educated Guess" Brown
+------------------------------------------+
| So we'll go no more a roving |
| So late into the night, |
| Though the heart be still as loving, |
| And the moon be still as bright. |
| |
| For the sword outwears its sheath, |
| And the soul wears out the breast, |
| And the heart must pause to breathe, |
| And Love itself have rest. |
| |
| Though the night was made for loving, |
| And the day returns too soon, |
| Yet we'll go no more a roving |
| By the light of the moon. |
| --Lord Byron |
+------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

Todd Bryan said:

Greetings to all. The original headset on my circa 1979 Miyata "Seven
Ten" frame is indexed and I want to replace it. I don't know if this
headset is ISO or JIS, and I'd rather avoid pulling the fork and races
to measure it. Are there other telltale identifying signs to look for?
The headset is unmarked, but it does have an odd 33 mm lockring.

The original in that bike is JIS

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971