I just used this site to get a better fitting filter for my '38. FYI the filters are listed by their exact size with the "by the inch" being the size range they are grouped in. For example if you click on 2" filters you'll see all of the filters from 2" to 3" in thickness. It lists the OD, ID and thickness. Pretty handy.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.