Reddit reviews Drillpro 400mm 8mm Lead Screw Acme Lead Screw and Nut for 3D Printer Z Axis

If you're going to replace the rods, you should really consider upgrading straight to lead screws. I replaced the m5 rods on my Prusa i3v with 8mm leadscrews and saw a pretty noticable increase in print quality. They'll help make your printer more rigid and have less backlash, giving smoother and more consistent print faces.

You can get relatively cheap ones off of amazon that will be a serious upgrade over threaded rods: https://www.amazon.com/Drillpro-400mm-Lead-Screw-Printer/dp/B017AR5QBS

I bought these lead screws. Be careful because they will not fit by default. You will have to drill/dremel out the existing z-axis mounts where the original threaded rod brass nuts were to make these fit. These take M-4 screws while the old ones took M-3 so the holes will need to be enlarged on the carriage. It took about a couple of hours to mount it correctly. It seemed that everything the Geeetech came with was too small by a couple of mm. The 8mm spring couplers were not exactly 8mm so I had to purchase new 8mm spring couplers to get the new lead screws to mount to the z-axis steppers. You will also have to cut the rods shorter because these were 400mm. I also had to tap the M4 threads into the mounting nuts for these. this might not be required as yours might come tapped but I would recommend buying an M4 tap or a set of metric taps. These were a pain in the ass to install but they produced really top quality prints, anything better than I've seen come from my printer. I would say it's worth the bit of engineering to get them to fit. I mean that's what this hobby is about right?

Mine printed fine for a couple months until I got lines like those.... I bought a new lead screw on amazon for about $10 and it’s been printing fine ever since.

https://www.amazon.com/dp/B017AR5QBS?ref=ppx_pop_mob_ap_share

This is the one I bought.

ACME thread leadscrew