O-Sizer Tape

O-Sizer Tape is easy to use.

  • First, take your O-Ring and determine its cross section. Each O-Sizer tape (OST-10, OST-19, OST-26) has a cross section identifier that corresponds with the appropriate series which will give the correct AS568 dash number for the O-Ring.


  • As you can see in the picture below, the O-Ring has a .139″ cross section, which makes this a 200 series dash number.



  • Once you have determined the cross sections, coil up the O-Sizer tape (OST), keeping the arrows on the outside, and insert inside the O-Ring. Let the OST uncoil to where it fits the inside diameter (ID).
  • The arrows will line up and give the the appropriate AS568 dash number.


  • This picture shows that I have a N70-258 O-Ring.*Flip the O-Sizer tape over and you will be able to size Metric O-Rings*

Metric Side



Available in Yellow (OST-10), Green (OST – 19) and Blue (OST – 26)