Composite position of hole pattern on cylindrical part

[Wuzhee]

Hi.

Question is about 4x M5 holes location in image below. Am I right that Datum B doesn't lock rotation in PLTZF? And it doesn't take part in the lower FRTZF (just have to be there),
Datum A locks 1 translation, 2 rotation
Datum B locks 2 translations
Datum C locks 1 remaining rotation.

If I don't lock my pattern to C the 4 holes could rotate freely around Datum B, is it true?

 

[greenimi]

Per 10.5.1. (3) / ASME Y14.5-2018: In some instances, the repeated datum feature references may not constrain any degrees of freedom; however, they are necessary to maintain the identical datum reference frame, such as datum feature B in the lower segment in Figure 10-43.
So, if you want to add C on the lower segment (to stop the rotation) then B is needed even technically is useless (as described above)