@eytec : You are agree with me resolution is 6.25µm

But on 3Drag datasheet, it’s the same it’s specified :
Accuracy Diameter of nozzle 0.5 mm, - X e Y: 0,015 mm - Z: 0,39 µm Diameter of nozzle 0.020”, - X e Y: 0,00059" - Z: 0,39 µm

So half as K8200 (0.781µm). From where this value is coming from ?

PS: sorry for mistake on screw size M8 and not M6, and for calculate value 6.25µm and not 0.625µm, I search to find orign of mistake and I made mistake !!!

Yes full stepp size is 6,25µm but the stepper driver are coded to 1/16 of Full stepp
so 1,25mm / 200 / 16 = 0,390625µm
why they write down the 1/8 Full Stepp (0,781µm) ?

I think this resolution is not possible with a normal z-axis (tollerace) so they double this