340 rod bearing size?

[Rocky_JS]

I pulled apart my 340 to freshen it up. The bearings are marked
tm77 .001 "OS" - Clevite 77's obviously.
The problem is when looking for new bearings for the engine everything I can find in a .001 states undersize?
Am I reading this wrong, or can anyone help me out with this?

 

[fishy68]

Since a crank journal is considered undersize when ground, they call any bearing other than std. "undersize" even though it actually has more material.