This cone allows easy measuring of rubber O-rings inner diameter.

Just place the O-ring onto the cone and read the diameter on the cone.

For example, O-ring on the sample photo has 27mm inner diameter.

Measurable range is from 5mm to 40mm with 1mm increment. This will not allow precise measuring of O-ring with Imperial or fractional metric size, but +/-0.5mm tolerance is sufficient for most practical purposes.

The cone is 3D-printed with advanced technology with high resolution that provides nice appearance.

Hollow interior to reduce weight (31g only). The flat base allows mounting it to a table if necessary, though handheld usage seems to be more convenient to me.

Total height is 159mm. Step height is 4.2mm that allows measuring O-ring with up to 8mm section diameter.