FORD 2008 F-550 v.1 - Manual (Page 351)

Replace the spark plugs with ones that meet Ford material and
design specifications for your vehicle, such as Motorcraft or
equivalent replacement parts. The customer warranty may be
void for any damage to the engine if such spark plugs are not
used.
3 Also available with 6.4L diesel engine and TorqShift transmission. Part
number is FT-176.
4 Also available with 6.4L diesel engine and TorqShift transmission. Part
number is FT-175.
2008 F-250/350/450/550 (f23)
Owners Guide (post-2002-fmt)
USA (fus)
Maintenance and Specifications
351