This is a replacement part for the runner for Franklyn brand blinds. May fit other blinds.
http://www.franklyn.net.au/indoor-blinds/panel-glide

For this part, you need to salvage the pin and the wheel, and insert them into the runner like the original. They should be firmly friction fit in, so they will need to be tapped in with a hammer.

I had 18 of these break off of my blinds after becoming weak from sun damage. Replacements can be bought here: https://www.blinds2go.com.au/shop/panel-glide-blind-runner/
however they cost 3.50 for a bit of injection moulded plastic which seemed ridiculous to me; hence the part.

Print with support for the gap where the wheel goes. I needed to print with a 3mm brim to stop the ends lifting.

Hope this helps!

Ps im planning on sketching up the other plastic parts like the catchers. Stay tuned.