O Ring Gauge O Ring Measuring Gauge AS568 BS1806 Range O Ring Sizing Gauge O-Ring Gauge Use for AS568 BS1806 standard O-Ring Sizing. Determine o-ring sizes in all AS568 standard cross-sections up to 13 inch ID O-ring. Made by High Quality Materials To Ensure The Reliability. The AS size number is shown in one of the small windows near the top of the main body. AS 568 sizes: 001 to 050, 102 o 178, 201 to 279, 309 to 382, 425 to 455.