AS568 400 Series O-Rings — 0.275 in Cord

There is no small 400-series ring. The lighter families cover everything below, and this one begins where a cord of this thickness finally has somewhere to go.

This family contains the sizes whose inside diameter tolerance the two source tables disagree on. On those pages that one cell is left blank and marked rather than filled from whichever table came first; every other dimension and tolerance on them is confirmed by both.

This is 51 dash numbers, from the -425 at 4.475 in (113.67 mm) inside diameter to the -475 at 25.940 in (658.88 mm). Every size in it carries a 0.275 in (6.99 mm) cord.

The numbering in this family is continuous across -425 to -475: there are no missing dash numbers inside the range.

2 sizes in this family have an inside diameter tolerance the two source tables disagree on (-469 and -470). Those cells are printed blank and marked, and the reason is given on the page.

Inches are the standard’s own units; millimetre values are conversions — inch × 25.4, rounded to two decimals — and not the ISO 3601-1 metric sizes. Outside diameter is a reference value derived as ID + 2 × cross-section; the two diameters the standard fixes are the inside diameter and the cord.

Tolerances are the per-size figures the standard gives, not a value derived from the diameter — the same inside diameter can carry a different tolerance in a different series, and each page prints its own.

Every dash number in this family starts with the digit 4, which is what puts it here. The remaining two digits are its position in the family, counted upwards by inside diameter — they are not a size code, and nothing in them can be multiplied or read off to get a dimension. Two rings whose numbers differ by one can differ by a hundredth of an inch or by a quarter of one.

A cord family is named for the cord its sizes are built on, and the name is a fair description of every size in it only when the family has a single cord throughout. This one does — it carries 0.275 in (6.99 mm).