[Closed] Hope is to is mount measurements

I've got a quick question on how the Hope is to is 20mm adaptor is measured is it the longest side between the 2 bolt holes or the shorter side? I'm asking as I'm trying to setup a rear disc and tried a mates adapter and he assures me that it is a 20mm adapter but when I measure the shorter side it is 20mm but the longer side is 40mm so I'm confused.

The issue is that the adapter that he gave me seems to increase the rotor size that I need from 165 to bigger than the 185 that I was expecting.

Any help greatly appreciated!