Lubricate the Threads
If you lubricate the threads, there is lesser friction between the parts. In this way, you can use a tapping fluid or a machine oil. They all will do the work. If you have nothing else, just use your saliva to reduce friction. With the help of a little lubrication, the job gets easier.
Spend Enough Time
You cannot rush with a tapping process. Make sure that you take your time when you are working with metric thread taps. When you are breaking a metric thread tap off in a hole, you will get annoyed and frustrated after some time. However, you must know that metric thread taps are hard so it will take time to drill it out. Just go slow and spend enough time on it.
Using the Right Hole Size
When you are drilling a hole, you will get a chart with your supplies that will have the correct drill size for every hole size. If the size of the hole is too big, the thread roots will be shallow and they may strip out. On the contrary, if the size is too small, the metric thread tap will bind and break.
Get a Metric thread tap Drill Chart
If you do not have a chart for metric threads, you can get it online. Just search for it online and you will find it for free. Simply download it in your phone or get a printed copy and paste it in your work space. This chart contains all the threading information that you require.