O-Ring Gauge

The BS or AS size number of small O-rings can be found by matching them with the silhouettes along the sides of the gauge. Larger O-rings are placed around the two halves of the appropriate spindles at the top of the gauge. The slide is then extended until it is taut, and the BS or AS size number is shown in one of the small windows near the top of the main body.
Used to determine the size of standard BS1806 or AS-568 O-rings
Section size identified by using the slots at the top