The new Pursa i3 mk2 uses lead screws for Z-axis. If you download and print the mk2 version files, you will notice the lead screw nut is missing. The TR8x8 bronze nuts that you can find in relevant stores don't match the screw holes of the x-end parts.
I spent a lot of time downloading and printing relevant nuts for the lead screw but with no fun as nothing would print to a nice fit with the leadscrew.
I decided to designed one from scratch. After reading Wikipedia on
Trapezoidal thread forms I designed according to spec and then printed and tweaked many times until I had a perfect result.
The file I have available for you is the already tweaked, ready to print nut.
I designed this to be printed in Nylon and used Nylon Bridge for my tests and final result.
I hope it works for you too ! I have the source file available should you want to tweak further.
Let me know of your results.
Update 6 May 2017 -- I also added a T8x2 version as someone requested it but unfortunately I cannot test since I can't source a T8x2 rod. If anyone prints it, let me know.
Update 18 October 2018 -- Thank you everyone for your comments and suggestions. Few people mention it fits MK3 (thank you biermeister for confirming) so I updated Title adding MK3. One thing to mention is I still use the first ones I printed back in April 2017. Don't forget this is not a true copy of a trapezoidal nut, its a modified printable version that was tweaked based on my printer on Tallman Nylon Bridge. Using different printer/settings/filament you should expect different results.
The Nylon Bridge settings that work for me are
Extruder 255 degrees
Bed 60 degrees with PVA stick glue
Cooling 20% fan after 1st layer
A little Wikipedia reading and countless hours of print-test-tweak-print