AMuzi wrote:

People have devised different styles to do that:
https://www.bicyclehero.com/media/ca...d/8/4/8475.png

http://images.modernbike.com/256/main_2126212142.jpg

https://fasterbikes.eu/738-thickbox_...pare-parts.jpg

http://www.ucycle.com/merchant/2856/.../Capture47.PNG

and of course the original design:
http://i.ebayimg.com/17/!BnNUOswCGk~$%28KGrHqUOKicEtluYLPB6BLio-KnEdQ~~_35.JPG

the exact shape doesn't matter except where
axle-to-frame position is critical, such as
inside-cable designs like this:
http://cdn.modernbike.com/Product_Im...arge_49040.jpg

which are color-coded for various angles.

They look mostly the same to me. Partly flat
axle hole, sometimes with a protruding part
as well.

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underground experts united
http://user.it.uu.se/~embe8573