Here is a rather nicely machined bicycle part. A square taper bottom bracket by Tange Seiki, the LN 3922. A surprisingly beautiful part given that it’s not hardly visible when installed. Made in Japan says quality. Just look at all the shine and precise looking machining:
Weight: 295 grams
Sealed Cartridge bearings
Solid boron steel spindle
JIS square taper
68mm English threaded
Comes in many sizes, this one is 107mm
What is a bottom bracket?
The bottom bracket is basically the bearings that are installed in the bottom bracket shell:
They make the crank spin nice and smooth. There are many different kinds, this is an older type, but one considered very durable and reliable. It’s threaded on one side and has a threaded sleeve for the other. It is screwed into the shell. As you can see in the pictures, it requires a special bottom bracket tool which has 20 teeth like the Park Tool BBT-22. The arms of the crank attach to the spindle which spins smoothly on bearings. Newer cranks have the spindle as part of the crankset, and the bottom bracket are the bearings you thread on.
Tange Seiki has been in making steel products since 1920. With all that experience I’m confident they know what they are doing.
I’m planning to use this on my Surly Cross Check bike build and will report back after I get some miles on.