Z-plus upgrade screw sizes

Starting the upgrade to Z-plus, my Y and X rails are not tapped. Metric screws in package say, m4x6 sh,m5x8 sh and m3x6 fh.Pulled out metric tap set and it gave me choices, big mistake? 4mm x.70,4mm x 75, 5mm x .75,or .80, .90. How do I determine the correct tap number for screws? Thanks to anyone for help.

The screws should be the standard metric coarse threads, which are M3 x 0.5, M4 x 0.7 and M5 x 0.8. If your tap set has a thread gauge, you can check the thread pitch of the screws to be sure. Threads other than the coarse ones are pretty uncommon for this type of machine.


Thank you the education on metric screw ID! I’ll try it. Not sure why so many choices in my tap set? I did not any scrap aluminum to test on. Thanks again.

Yes metric is very easy. The M5 .08 is metric 5MM Body and .08 threads per MM. There are many charts on the internet that show what drill size to use for a given metric bolt you want to thread. Many times the the metric size like for M5 is 4.3MM. Not many people have a 4.3MM drill so you would need to drill either a 4MM or 4.5MM hole is you have an assortment of drill bits in metric size. You could also find a SAE to metric conversion chart and find a Imperial drill size close enough.

There are two type of taps, through and bottom. The through taps have a taper in the beginning to help you ease into the drilled hole. The bottom taps have the same size threads from top to bottom so if you tap a hole with a bottom tap the threads go all the way to the bottom of the hole. A through tap may not be long enough to thread into a hole that is not through. You would get maybe a few threads and when it hits bottom and it might break if you apply too much torque creating a problem for extraction. The rails are hollow and the through taps are best and most common to use because of the taper at the beginning.

When tapping use oil on the tap and twist a turn or two and then turn it backwards and then go forward. This helps clear the chips out of the hole. They make Tap Magic cutting oil but just about any oil helps like 3 in One Oil or even motor oil.

Also use a center punch when you mark your holes. This keeps the drill bit from walking and you get your hole where it is supposed to be.


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