I am building a Prusa i3 MK2S (Dolly). I find it very difficult to find M5 rods for the Z axis, I have an M8 lead screw with 8 mm lead, So I thought since M8 is widely available online I could just use them instead of M5. What do you think about it? What should I keep in mind?

as long as you match the parts that is ok. The m8 rod will give you more stiffness and will be harder to bend. As the result, you will have to calibrate the steps/mm settings in the firmware.

• Do I need modified dolly parts for m8 lead screw or the original dolly or standard parts would work with them???? Mar 21 '18 at 4:40

Amazon has a few hundred M5 rods listed for sale, so I don't know where or what you've been looking through.

If you change the lead screw, you'll have to change the threaded parts on the gantry assembly to match.

More important, you'll have to adjust the Z-drive "steps/mm" setting to match the 8mm lead. (with thanks to Professor for pointing out my error)

• there is no need to change g-code. There is a need to update steps/mm settings Mar 5 '18 at 17:24
• "Amazon has a few hundred M5 rods listed for sale, so I don't know where or what you've been looking through" Hi Carl Witthoft, I am from India and Amazon.in doesn't sell the rods much, its hard to find one good seller. Mar 6 '18 at 9:22

You can use the screws and rods you can find easily, of course some dimensions will change and is needed to adjust parameters.

I used in my first 3D printer and standard screw of 9.5mm (3/8) the main problem was the coupling available in Mexico that werer none on that time.

You can buy the bearings on Ali Express, they can send from there to Mexico, I guess they can deliver on your country.

The bearings has these sizes:
where is Number ID, inner diameter, outter diameter, width.

608ZZ 8x22x7
607ZZ 7x19x6
6000  10x26x8


Don't try to use 6000 :D is a little complicated to reduce the size for a proper coupling if you don't have a lathe. My 3rd Printer will use this kind of thread because is easily to find with no warpage and now I will use a lathe to reduce the coupling area to 8mm or 5mm since I have on hand the couplers.