Best description I can give is Dad’s sketch of it (here).
All he could say was that it was the shape and size of a large knife or dagger, but with a blunt tip and edges. There were notches along its length, which ended in little circles.
The best anyone he showed the sketch to so far was that it was used by weavers.
Any ideas would be appreciated by Dad.
I don’t see a picture when I click your link.
As I’m a weaver, I was hoping I could give you an answer.
It sounds like a weft beater from your description - a device used to push the weft threads tightly and evenly into the warp threads
Not sure what happened to the link there, sorry.
The notches in the tool aren’t at the end but at right angles along the shaft.
It appears to be a sheet of carbon paper.
Well done, sir.
It is hard to tell from the picture; does it use AA batteries or C batteries?
I clicked all over the page to try to save an image and work with it. There are no images on the page.
From your description, it sound like it could be a sleying hook, which is used to thread the heddles on a loom and draw the warp through the reed.
Do a Google image search and see if anything fits.
ETA: Oops. Missed the part about the notches being at right angles. Probably not a sleying hook, then.
The original URL worked for me, but here is a direct link to the image:
http://farm8.staticflickr.com/7167/6612363849_4a76593e05_b.jpg
I never thought that looked obscene till I posted it on the internet 
Your dad has a dirty mind.
Where did he see this tool? Under what circumstances?
Can he get a photo?
Speaking of weaving references that come across oddly…
Have you stopped beating your weft?
Is it possible that it is the handle to a jacquard heddle? (Mouse over to see enlarged view.)
Most “solid” heddles tend to be flat pieces, like this, or like this.
The jacquard heddle looks to be a bit more complex.
