8mm m8 threaded rod

What lock nut do I need for this rod?
I tried 8m x 1.25 and the pitch is wrong…

This is to replace the 5/16 rod with a typical reprap rod…

Yikes and I met coupling nut

I believe that M8 only comes in two pitches - 1.25 is coarse, and 1.0 is fine pitch. Someone can correct me if I’m wrong, but I would get M8-1.0 for the Z axis. That means that your threads are 1.0mm apart (I hope I’m not over explaining - I just try to be thorough).

FWIW - for Imperial hardware the Parts page says to use 5/16-18 which is the coarse thread version of 5/16 - https://v1engineering.com/blog/parts

You will have to adjust your firmware either way, so maybe it doesn’t matter. I believe I have fine pitch for the Z axis.

Where do I get the coupler for the lead screw m8? I only have seen m8 - 1.25 which does not work

I think I misunderstood you. Are you trying to use a lead screw or M8 threaded rod with a coupling nut?

If you are talking about a lead screw, you could try this thing along with a lead screw nut, but I have no idea if it would work since the designer hasn’t even tried it: http://www.thingiverse.com/thing:1727299

(On that note, I can’t find a M8-1.0 coupling nut. I would just buy threaded rod that is M8-1.25, or stick with 5/16.)


I was able to fix this by purchasing a 8mm 2mm pitch lead screw on amazon. It came with the coupler (round).

T8 300mm 8mm Lead Screw with Coupler

I then bored out slightly the top piece for the Z carriage assembly and inserted the coupler into the top. This prevented the restraining bolt to completely screw down, but it was through the whole assembly and allowed rigidness.
See Pictures of the assembly with the coupler and lead screw installed.

I had to update the firmware for the Z steps reducing to 800.

I then added grease to the lead screw and ran it up and down a few times. raising it 160mm each way. This allowed pushing the grease through all the threads.

I the lowered it and zeroed it as we normally do…

Did a test print - Viola! perfect horizontal prints… wow in fact you cannot see the lines at all… barely at .2mm
RECOMMEND this solution over the supplied 8mm or 5/16 solution… as its ridged enough to never be bent and is incredibly accurate.

Before you recommend it make sure it works with a heavy router and you have a look at the FAQ’s.

I guess my actions proved themselves… Ryan is now promoting this solution lol

The positives now outweigh the negatives, from a production standpoint. A bunch of you have been using lead screws now, a few since day one. None of you have complained about the need to constantly replace the brass nut so I feel they must last long enough to not worry too much about it as a consumable part. A vast majority do not have any issue with the allthread and can easily save some money by using the easier and cheap to source allthread.

Cheap leadscrews still bend or come bent, accuracy has a price. Lead Screws with a certified straightness cost about as much as the full kit.

I am still very careful not to say this is the best way, just the way I chose to sell future kits. I have written a fairly long post about this. Ballscrews are still the correct way to do this, allthread is the easiest, leadscrews are the sweet spot in the middle.