I have SW2016.   I have two parts in an assembly.  I've created a new third part under the assy for a join to create one part.    However, in 2016 - I pull down "Insert" and there is no features option.  I used the customization to grab the join command onto my tool bar.  But when I have the new part selected for a join, the command is greyed out.   The procedure under help does not seem to work.

Thanks in advance,

Bill