Aluminium grade

Hi,

Did my homework. Searched for aluminium grade, found nothing.

My question: What grade aluminium to use for making fixture (for cnc
machines)?

Reason for asking: got some aluminium from supplier - 6061. Was told
that there were 2 grade, and there was another cheaper grade. So I
assume 6061 would be harder.

However machining shop told me the aluminium I got was softer than
the one he normally get from his supplier but could not tell me what
grade. So what grade of aluminium should one get for making fittings
for home-brewed cnc machines?

Thanks

Pete