I have a couple of them Harbor Freight o-ring kits.  They don't work on hydraulic blocks.  

  I got mad last time and ordered a couple  500 piece 90 Duro O-ring $30.00 kits. A metric kit and a fraction kit.

  When I had to drive to town and get one, the package says it is 90 Duro, what ever that is. I think hardness or toughness.