Thank you for posting part numbers
I looked up the Centric 14166021 on RockAuto.
You obviously measured the piston diameter as >3.25" (perhaps 83mm) and showed us the picture. Thank you.
Similarly, another GMT400 member had stated earlier this year that the DRW caliper piston diameter is ~3.28 IIRC, i.e., the same thing as your picture shows.
RockAuto's database for the Centric 14166021 shows a larger piston diameter, which suggests their database is somehow incorrect. I've posted it, below.
|Piston Diameter (IN)||3.386|
|Piston Diameter (mm)||86.000|
A cursory review on RockAuto of other
mfgr's calipers for the DRW GMT400 regularly turns up the "3.386" / 86mm" numbers as well. Earlier this year I actually quoted these stats in a couple of other posts on GMT400.
Your pictures don't lie. I wonder why the disparity with the mfgrs' stats... not just one mfgr, but multiple.