leadscrews and threaded rod Prusa I3

[BassmanJ74]

Hello all, I'm hopeful someone here will be able to help.

In my first venture into 3d printing I've bought and assembled one of the Prusa I3 kits. I was having a lot of problems with the Z axis refusing to move.
On removing the threaded rods I found they were bent leading to the Z axis seizing up.
I've bought and fitted couple of leadscrews which has sorted out the movement problem, however the threads per inch on the leadscrew is very different - one revolution of the M8 threaded rod gives a lot less vertical movement than an 8mm leadscrew.

I'm guessing I need to change something in the software somewhere to re-calibrate the movement?

Can anyone please point me in the right direction?

Geeetech Prusa I3
Arduino
Marlin
Repetier host

[BassmanJ74]

Nevermind, in the 2 days it took for this post to appear on the forum I've resolved the issue.

[_kaktus_]

Metric screws, eg M8, are not suitable for such applications.
You should purchase a trapezoidal screw with an appropriate thread pitch.