From EBMM FAQ
Q: Which strings do you use at the factory to string up your guitars?
A: The Ernie Ball strings we use on all of our guitars is as follows:
Silhouette & Silhouette Special: RPS-9 Slinkys (9-42) catalog #2239
Axis: RPS-9 Slinkys (9-42) catalog #2239
Axis SuperSport with DiMarzio humbuckers: RPS-9 Slinkys (9-42) catalog #2239
Axis SuperSport with MM-90 pickups: RPS-10 Slinky (10-46) catalog #2240
Steve Morse: 10-13-16(all RPS)-26-32-42, available in single strings only
Albert Lee: 10-13-16(all RPS)-26-36-46 available in single strings only
Luke: RPS-9 Slinkys (9-42) catalog #2239
John Petrucci: RPS-10 Slinkys (10-46) catalog #2240
Benji Madden: 12-16-(RPS) - 24w-32-42-52 available in single strings only
SUB-1 guitar: RPS-9 Slinkys (9-42) catalog #2239
The John Petrucci 7-string guitar uses RPS-10's with an added .56 nickelwound for the low B string. A suitable replacement set is the #2621 7-String Regular Slinky set (10-56).