I'm looking for a new 24mm rear axle nut, sprocket side. When I look at the parts schematic on the OEM parts website, it appears that the part is integrated into the rear axle itself. This is not the case for my bike; it is a separate 24mm nut that is threaded onto the rear axle. 2011 Honda CBR250R 2AC REAR WHEEL | Babbitts Honda Partshouse Part number 3 to be exact. I'm a little confused.

From what you're describing, it sounds like the axle on your bike was installed from the brake side of the swing arm, instead of correctly being installed from the sprocket side of the swing arm. Anyway, the axle nut you're looking for is Ref# 20 in the link you posted.

it says that nut is 10 mm? the nut I need to replace is 24mm and isnt listed? Its the axle nut (24mm) you have to loosen before making chain adjustments.

the nut on the brake side is 16mm.

the nut shown here is the one im looking for. It is shown installed on the sprocket side.

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excuse me the nut on the brake side is 19mm; this is the nut that is integral to the rear axle.

You've got things a little mixed up here... the 10mm nut you're talking about is used to secure the rear sprocket to the Driven Flange. Notice that this nut shows a quantity of 6... whereas there is only 1 axle nut.

Nuts and bolts are identified by the thread diameter and thread pitch, not by the size of the wrench used. So the 16mm nut listed as Ref# 20 is the axle nut, and yes it uses a 24mm wrench.

The axle bolt has a 19mm hex head on one end... it is not a separate nut.

You are correct regarding the axle nut being on the left (or sprocket side) of the swing arm, and the axle bolt going through from the right side (brake side) of the swing arm... that's also how it is installed on my bike. For whatever reason the CBR250R Parts Diagrams are showing the axle bolt as installed from the opposite direction. Not sure if it even matters which direction the axle bolt is installed from. Probably six of one, half dozen of the other.

Oh, that makes much more sense; sorry I was unaware of that! I appreciate your consideration, you have been very helpful! Thank you.

If you are new to mechanics in general, then there will be quite a lot to learn.
You are more than welcome to ask your most basic questions here, that is why we are here. But you might look around the area high schools for a night class in automobile shop mechanics. Sometimes you can even find one for motorcycles, where you work on your own bike!

M/C ownership - you'll love it
It's a way of life!