Class II hose stations are typically 1-1/2". Replacing Class II with a Class I hose station permits the use of the smaller 1-1/2" thread but requires a reducer from the mandated 2-1/2" thread required of a Class I.
Personally I've never installed a Class II hose station; the AHJ has always requested a Class I.
I believe Stookey has commented on Class II hoses being removed from the code someday as fewer and fewer buildings have trained personnel to handle fire hoses.