No idea if I'm missing some kind of cotter pin or some other type of fastener. This is the right side front forks. Those holes look like there should be something in there.

 

Theyre there so you can stick a rod, screwdriver or whatever fits to hold while loosening and tightening the nut on the other side if the axle...surprisingly harley doesn't sell a 50 dollar piece of chrome to fill that hole though lol

 

43583-09 "COVER, axle nut (black) (2)" is for FLSS & FLSTFBS - might fit your model. Billet apparently. I see them listed at $22.99 each.

 

Designed that way, Makes feel like I’m riding on the edge

 

If your front wheel bearings go out...you'll get very familiar with that hole...

 

That hole there that runs front to back is to stick a 7/16" drill bit in so you can tighten the other side. It's an alignment aid.
It's in your Factory Service Manual.

 

I would think a drill bit might be uncomfortable, brittle, or too short. Not sure what alignment is being done when doing up the nut on the other side.

 

Make sure the hole points forward, so the air can get through easily, good for 3 mph at top end.

 

Fair play!

2008 & 2017 Sportster FSM went with steel rod.