Chevrolet Repair: wiper arm, stranger things, allignment

Question
I need to replace the wiper arm on my 2001 Venture
I bought a new arm but I see no spline threads like on
the shaft it attaches to. Do I just put it on and
crank the nut down as hard as I can to make threads?
I would hate to screw this up I was forced to go to
a dealer and pay way too much( to much snow here to look at junkers) and I need to get to work  

Answer
Hi Kevin,

I have been trying to do research for your question, and time kept getting away from me.  I have changed wipers on this type of set up before.  However, not specifically on the Venture.  I didn't want to tell you wrong.  

I intended to call the dealer today.  However, I got busy and forgot.  I will give a follow up if I find out something more than what I am about to tell you.  

On those type of wiper arm, I cannot believe you are supposed to just torque the bolt/nut down and create your own splines.  Stranger things have happened, and it is possible that is the way.  However, I have only dealt with splines on both the arm, and the shaft.  You actually are supposed to match them up for allignment.  There is a large one you match up.  Sometimes though, there is not an alignment spline, and you just keep installing the blade until it is right, when it runs.  

I am sure you fixed this by now.  You said you needed it for work.  But if not, and still unsure, I would wait until you know for sure, before you create your own splines.  

I wish I had more for you.  Sorry:-(

C J S