I'm pretty sure it's "kief"

Look at this:
http://www.everyonedoesit.co.uk/onli...CategoryID=730

But I really want to try a kief tumbler. I think I can make one for much less than $518 though.
http://www.everyonedoesit.co.uk/onli...CategoryID=776

The consenses seems to be silkscreen to sift out kief. There are many sizes. I noticed the tumbler above uses 150 micron. Is this how silkscreen is measured, and is this the right size?