New CNC Mill on the horizon

[JAZZCNC]

I use M8 for bolting together the Gantry your copying. M5 for fastening profiled Linear rails.
In general you'll need an assortment of M5,M6, M8.

Depending on how your fastening Steppers then you may want M4 But I tend to use M5 and tap the stepper. If your bolting thru stepper then some times depending on stepper frame M5 socket head will touch motor side, not always but does happen. I just whiz head against bench grinder rather than use M4. I try to keep different bolt sizes to minimum, fewer tools needed and less variety of bolts required.
If tapping the stepper you can use M6 without any problems but M6 is no good for bolting thru stepper has head is much too large.