From inside (document excerpt):
IllUSTRHTfD PHRTS liST MODELS SERIAL NUMBER PREFIX MODELS SERIAL NUMBER PREFIX 600017B 600017C 600017F 111111- 600016G 600017U 1411- MAC 130 CHAIN SAW McCulloch chain saws are identified by a model number (in this instance, 600017) followed by a suffix letter (A, B, C, etc.) stamped on the identification plate attached to the saw. Suffix letters denote variations in parts or assemblies in the manufacture of the saw. Part numbers listed in this I.P.L. which have a suffix letter or letters following the description, indicate the part is used only on the model(s) identified by the letter or letters.
Part numbers and descriptions without suffix letter or letters apply to all versions of the chain saw model. Part numbers which have one or more dots (.) preceding their descriptions may be ordered individually, but they are also included in the kit or assembly whose description begins directly above the dot(s).