Symmetricity and using hole as Datum

[prascena]

Hi,

New to this. May be very basic, sorry.

Can anyone please help to understand whether the below used GD&T is right? Can symmetricity be defined without calling out to which datum? If the hole needs to be used as datum but have symmetricity, how do I define

[Kelly_Bramble]

Assuming an ASME standard then yes the center line of symmetry symbol is used correctly.

See:
ASME Y14.5M - 1994, paragraph 1.8.8 and 1.7.1, fig. 1-33
ASME Y14.5-2009, paragraph 1.8.9 and associated fig. 1-35
ASME Y14.5-2018, paragraphs 4.5.9 and 4.4.1 and fig. 4-33

The only real issues I see are:

If this is an ASME specified engineering drawing and Rule #1 is invoked then the parallelism tolerance is greater than the limits of size rendering that specification meaningless.

The two hole features ( 2X dia.9 H7) specified should most correctly be specified to a perpendicular and not a position tolerance. Though position gets the message across.

Hole features should probably have a "thru" indication or show hidden lines in the top view.

[paulmartin1492]

In addition, the rotational degree of freedom about datum B is not constrained. Consider adding a datum C.

[paulmartin1492]

Ignore my previous post. Datum B is along two holes so rotation is constrained.