we are offering o ring. there are several different standards to choose from when it comes to o-ring dimensions. the most popular in the united states is the as568 standard for o-ring sizes and tolerances. maintained by the society of automotive engineers, this standard allows the user to choose from five different cross-sections with inside diameters ranging from 132" to 26". tube fitting boss seals are included in as568 as 900 series o-ring sizes, and are intended for use in ms33649 (now superseded by sae-as5202) straight thread tube fitings.cross section tolerances0. 0 0 to 1. 8 0 0 .0 81. 8 1 to 2. 6 5 0. 0 92. 6 6 to 3. 5 5 0. 1 03. 5 6 to 5. 3 0 0. 1 35. 3 1 to 7. 0 0 0. 1 5general properties of elastomer classes & rubber compounds: