my dirt merchant rear fender recently died and broke off... perhaps it was tired of living as it promptly scuttled under a nearby car and took me a bit of time to retrieve! anyhow i decided to disappoint it by creating this mount and dragging it, kicking and screaming, back into service. (you will have to die another day, dirt merchant!)
This is an adapter to mount a particular kind of rear fender (a blackburn dirt merchant) to the swingarm of a particular mountain bike (a specialized 05fsr xc comp). as you will notice from the pics, i have some incredibly small 1.25" road tires mounted on my 21" rims, so with the mount, the fender will not clear normal knobby MTB tires.
chances are, few of you will happen to have this combination of bike / fender / tires lying around, but perhaps this part will serve as a decent basis for your own design - it probably would not take much work to adapt it to another dual suspension bike, or perhaps add parts to be able to print a full rear fender?
in the pics i left the part in orange for clarity, although i will probably spray it black.