Sharpening choil, slipjoints vs other knives

[Hengelo_77]

On most knives sharpening choils are round(or half a found file)
Exept on most slip joints, their sharpening choils are usualy triangular shaped.

Is there a reason for that or is it an old tradition?

 

[Britmaker]

Tradition by makers who wanted to make life easier for them producing a clean sharpened edge. They are generally a hindrance.
My most carried pocket knife is a Canadian Russell and, when new, had a very small choil. After a good number of sharpenings it is now perfect with no choil.

 

[silver_pilate]

Can't speak to the tradition of it, but I'd avoid an angular choil as it can create a stress riser.

 

[Drew Riley]

I often do a "triangle" choil on my slipjoints as it is a bit more traditional/looks better to my eye. That said, I always radius the inside of the notch to reduce any stress risers.