Solid difference problem

The difference is the same size as the original, and widget doest make any alert.
Why?solid (31.5 KB)

Not the same volume for me in R6. Looks correct.

Your tolerance is likely too stringent
On my Rhino 7, when set to tolerance 0.001, SolidDifference fails and of course the two volumes are the same. When set to 0.01, the component actually cuts the geometry and returns different volumes.

thanks for the solution. I run into tolerance problem quite often.
I remember formerly I had a problem that if I changed the tolerance it caused problem with boolean operations on other part of the model. Is it possible that there is a model on which boolean operation cannot be done with a single tolerance value? (without changing the tolerance) Can you explain what is the tolerance about actually?