Why would this be in sewing box?
 

Someone found this in a sewing box and wondered if there would be some use for it when sewing.
Attachment 648680
It looks to be a replacement blade for a raspberry cane cutter. Any idea if it could be used for something else in a sewing room?

If the inside is sharp, I'd say a heavy duty seam ripper. Like for canvas or leather seams.
How large is it?
Otherwise, my guess would be that it simply ended up there "for now" until it got put to its proper place.

I think it is one of those "for now" places, too. I'm not sure how big it is, but looks bigger than would be needed for leather or canvas. https://www.leevalley.com/en-us/shop...ter?item=ED725
https://www.leevalley.com/en-us/shop...ter?item=ED726

There's all kinds of weird things in my sewing room! So here's a guess ...

... for cutting chopsticks, bamboo sticks or small dowels into usable sizes.
Kind of like a mini-saw.

It could have been mounted and used to cut chain piecing apart, back in the days before the little cutters that use old rotary blades.

I'll bet the person who owned that sewing box wondered where they put that!

That seems like something I would do. How often we put things for safe keeping and then forget where it was.

The person was a costume designer and had planned on using that in a pirate costume?

It is a replacement blade for a raspberry cane cutter. I googled it, exactly the same as pictured.