It changes through the model years and engines, but as for the 2006 model:
PR-codes:
PR-1BK+T15, T41,T81, T82, T14, T8T, T44 Anti-roll bar size
30,3X3,4 mm. Part number 4E0411305AA.
PR-1BK+T42, T1H, TB1 Anti-roll bar size
30,8X3,5 mm. Par number 4E0411305AB.
PR-2MA+T15, T41, T81, T82, T14, T8T, T44 Anti-roll bar size
30,8X3,5 mm. Part number 4E0411305AB.
PR-2MA+T42, T1H, TB1 Anti-roll bar size
31X4,7 mm. Part number 4E0411305AC
PR-2MB+T8E Anti-roll bar size
31X4,7 mm. Part number 4E0411305AC.
Out of this, we see that the 4.0TDI, 4.2TDI and W12 with sport suspension has the same size anti-roll bar as the S8.
1BK -> normal/standard suspension.
2MA -> sport suspension.
2MB -> sport suspension S8.
This was only for the front, and for the rear:
Here I don't have the size, but I can compare the part numbers.
PR- and engine-codes:
PR-1BK+BFM, BFL, BAR, BPK, BVJ, BHT, BSB, BSM, ASN, BNG, ASB has part number 4E0511407D
PR-1BK+ ASE, BHT, BTE, BVN, BMC has part number 4E0511407J
PR-2MA+ BFM, BFL, BBJ, ASN, BAR, BPK, BFM, BGK, ASB has part number 4E0511407J
PR-2MA+ ASE, BHT, BTE has part number 3D0511407B
PR-2MB+T8E has part number 3D0511407B
Here we see that the 4.0TDI and the W12, both with sport suspension, has the same rear anti-roll bar as the S8.
Not so complicated after all?
