After being in the auto repair buis. [ employee & my own shop ] for about 30 yrs. ,
The way I look at it is that , to think of all as 2-3 weight classes , becouse of the verity of parts that you run into when they need replacing .
Our trucks are a good example , the Dana 44 can be found in both the 1/2 & 3/4 gaser , but with the Commins , it starts with the Dana 60 , the 60 can be 3/4 & 1T ,
Then the springs have at least 2 choises , also , bearings , brakes , wheels , tires .
Some yrs. ago US cars started at 1/2 , now maybe as low as 1/8 .
It seems that the parts supplyers just change again , went looking for ajustable upper ball joints for my truck , talked to about 5 derrerant [ parts guys , from napa to the manufacture ] becouse they were hard to find , becouse they no longer look up the parts the way they did last time I did these , ex. they asked yr , mld , 3/4 or 1T , did not ask about eng. or GVW [ witch they used to ]