It is my understanding that the outside diameter of the adapter ring is the same size and that in all cases the ring acts as a step up from the lens filter diameter to the internal diameter of the filter holder. As there is only one filter holder size then the conclusion is that the outside diameter of the adapter ring is constant.
I guess the lens covers come in threes to cater for the practice of buying multiple adapter rings that you fit to each lens you own. Those tight-wads amongst us only buy one adapter ring per lens filter diameter and move it between lenses - so three in a pack does some excessive.
You can research more at
Lee filters web site. If you are still unsure then give them a call - their main operation is just south of Newbury, UK.
