ISO International Standard

ISO 3601-4:2008 specifies dimensions and tolerances for five types of anti-extrusion rings, which are also known as back-up rings:

1. spiral type (T1);
2. angle cut type (T2);
3. solid type (T3);
4. angle cut concave type (T4);
5. solid concave type (T5).

These anti-extrusion rings are for use with selected O-ring sizes as specified in ISO 3601-1 and the relevant housing dimensions specified in ISO 3601-2.