Question regarding Windshield Wiper Arm

Recently upon turning the windshield wipers on one failed to move from a certain point while the other continued as normal. Researched the issue and read where the mounting nut beneath the plastic cap can loosen and causes the wiper arm to slip or fail to move.
This is the case.
I’ve attached a pic of the mounting point on the failed arm.
My question is, in the pictured hole in the wiper arm are there supposed to be grooves or teeth that line up with those on the drive mechanism on the car? The lines are barely visible on the arm.
Or is it simply held on with a tightened nut and washer?
Appreciate any insight.
Bill
FL

Pic makes grooves look more prominent than they are.
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Definitely little teeth. You're in for a replacement arm and do tighten the nut that holds it.
Failures like this are usually the result of poor mounting, esp. tightening the nut while the male/female teethes have not engaged.

 

small dremel, deepen the grooves, new nut with engaged teeth, loctite?

 

Bill,
It needs replacement, is that the driver's side or passenger side?

Don't throw it away, I'll PM you about it later

 

Thanks so much guys! I figured it was going to be a new arm. The aluminum appears soft enough that it could almost be a tight fit type deal with the teeth on the drive mechanism digging in when being tightened.
New arm ordered from Ricambi.
There’s a lesson here. Pull your plastic caps and snug those nuts up before you are the next victim. A couple minutes max to check and or tighten them. Damage for one wiper arm, $165 ...and mine was the cheap side.
The plastic cap pulls off or if necessary can be pried off with a rigid credit card (won’t scratch). Pops right back on. Nut is 13mm I believe. I’ll look up torque values if there are any before reinstalling mine and post it.

Dave thanks always for your feedback. This was the passenger side wiper arm. I’ll wait to hear from you. I’m glad to hear there might be a use for it as was perfect minus the stripped teeth. Hated thought of tossing it.
Bill
FL

 

Posting the end of this story.
The passenger side wiper arm was no longer available (NLA) at Ricambi. Dave was kind enough to pass along a lead that there was a new and used wiper arm on eBay sold by Ferrparts. I took delivery of the new one.
The new matched my old. There are no splines on our wiper arms, well at least the passenger side. It’s just a cone type machined hole in aluminum. The torque of the 13mm nut sinks the splines of the drive mechanism into the aluminum arm apparently enough to do the job.
There was no torque number for the nut securing the arm listed in the WSM.
I reinstalled the arm, torqued to feel and should be good.
When initially trouble shooting the problem the 13mm nut was finger loose.

Note the plastic cover caps are also listed as NLA.

If anyone down the road needs a new Maranello right side wiper arm that’s NLA, I’m your guy.

Bill
FL