Whats it for?

 

 

Plastic injection molding manufacturing process I believe

 

You can buy attachments for it, including muffler bearings.

 

I was wondering the same thing, my aftermarket black housing headlights are identical to my OEM chrome housing headlights, except for that bump over the turn signal. Aerodynamics? Side visibility of the turn signal?

 

My guess is for turn signal/position light visibility from the side. That light also works as the front side mark light.

Edit: It's not the side marker light.

 

It refracts the light from the turn signal lamp so that the light is visible from both the front and from the side. Basically a low-tech beam-splitter.
It has nothing to do with headlight alignment or aiming.

 

its for mounting the headlight aiming tool.

 

Maybe discussing different bumps? We talking the big bulge over the ts or the little nubs you see on most factory lights?

 

There are no little nubs on these headlight lenses, and those little nubs have not been used for headlight aiming machines since early 90's vehicles.