It's my understanding that the arms are soft (pot) metal, the knurled shafts are hard.� As you install and tighten the nut, the knurls are cut into the soft arm metal, forming knurls as you go.

Rich
San Diego

--- On Sun, 9/19/10, John Rodgers <inua@CHARTER.NET> wrote:

From: John Rodgers <inua@CHARTER.NET>
Subject: Wiper Arm Knurling - How does it work?
To: vanagon@GERRY.VANAGON.COM
Date: Sunday, September 19, 2010, 3:16 PM

 I recently acquired a pair of replacement wiper arms with the airfoil
on them to replace the ones I have with no airfoil.� When readying to
install them, I discovered there is no knurling on the inside of the new
wiper arms where the knurled wiper shaft goes through,� as there is in
the ones I took off. In the replacements, it appears they have corroded
away, been worn off by abuse(nut not tight) or simply were never there.
In any case, without the knurling, it would appear that slipping would
be an ongoing problem. Anyone have any ideas as to how to address this
issue?

Thanks,

John

--
John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com