This article is from the Ducatis Motorcycles FAQ, by Duke Robillard email@example.com with numerous contributions by others.
907 owners using the older DR8ES spec jobbies are now using DPR8EA-9, with
reports of elimination of surging that seemed to appear around 4100 rpm and
more low rpm smoothness to boot.
851/888 owners used to the Champion A59GC are now using NGK D9EV spec plugs
M900 (Monster) and 900ss' are switching to NGK DPR8EA-9 or NGK DPR8EV-9
from the Champions.
Note: The Champion plug uses a 16mm drive and the NGKs use an 18mm socket,
so pick up a new on board plug wrench if you make the switch.
For those of you who were wondering, and those of you who weren't. Here is
the NGK Spark plug code straight from the book:
prefix D P R Thread diameter construction Resistor A : 18mm M compact type B : 14mm P projected Insulator C : 10mm U Surface Discharge D : 12mm Z inductive Suppressor E : 8mm 8 E A Heat Range Reach Firing End Construction 2 Hot E: 19mm A: Special Design H: 12.7mm B: Single Ground, Special alloy L: 11.2mm C: Dual Ground, Spec. Alloy F: Taper Seat G: Racing Type Z: 21mm GV: Racing V-Type Blank: L: Half Heat Range 18mm phi 12mm S: Standard Center Electrode 10 Cold 14mm phi 9.5mm V: Fine Wire Center Electrode X: Booster Gap Y: V-Grooved Center Electrode