How does one tell what type BB is on a bike. Bike in question is a late eighties well made Jap steel roadie. Thanks in advance. Lp

Check out Sheldon on BBs. The bible.

If you are talking about the threading and its japanese then it will take a regular bb. One thing you can do is measure the BB shell to see if it is 68, which I am pretty sure it is.

Another informative link, this one should be an intro to the abovementioned.