Already I am going to point out something:

1. Base and RS versions did not have a rear sway bar.

2. You say that a 13mm in the rear does not sound right and that it is 12mm? That 1mm is what tipped you?

3. By "searching on other sites" what are you referring to? Tuners? I am interested in seeing your references if you do not mind. Not saying I doubt you personally, however unless you took a dial caliper to all model sway bars personally I would like to know the source.

According to CAPS,

All FWD platforms share a rear sway bar part number of MR130722.
All AWD platforms share a rear sway bar part number of MB914340.

Non-Turbo models had a front sway bar part # of MB910391 or MB871885.
All Turbo models had a front sway bar part # of MB871885.

MB910391 is 16mm
MB871885 is 19mm

These are OEM specifications.

Think logically: Is a manufacturer going to spend money on producing and stocking three different rear sway bars and three different front sway bars for a total of 6 parts to share across trim levels of a vehicle? No.

---

2012 2500HD LML