Single SPEED! I hate how people in this forum think it's all fixed...
Looks like you got a late 90's acera hub.
Just get yourself a "standard Shimano cassette lock ring" that comes with any of their cassettes made within the last 10-15 years and it will work grand. You can get them from any bike shop. Just ask for a new one or old one from a junk cassette
There should be a really thin washer, same sized diameter coil spring and the lockring itself.
I've interchanged acera, deore, xt, xtr cassette lockrings no problem. They're all pretty much the same. Even the road ones might work.
It should look exactly like this (even thought this is a SRAM lockring), hell SRAM might even work too!
You'll need one of these to install it:
Shimano cassette/lockring tool.
However if there are threads on the outside end of the cassette splines (20 years old+) then you might be able to use an old BB lock ring. From what I remember it is the same diameter.
Last edited by lymbzero; 07-27-08 at 08:23 PM.