General information about Metric thread taps – steps and standards explained

Metric thread gauges

To build any machinery part, an engineer needs to join two or more different parts using screws, nuts, or bolts. A tap is a handy tool for cutting screw threads to make a hole where one can attach nuts or bolts. Metric thread taps also does the same thing. They come in different sizes for making holes of different sizes.

Important information about metric thread

Some common metric thread dimensions are M4, M5, M6, M8, M10, and M12. M4 indicates “standard” M4 thread size. In a case of a bolt, the external diameter of thread is 4 mm, while its pitch is 0.70mm. There also exist ‘non-standard’ M4 threads with different pitches. Non-standard M4 threads are not compatible with standard M4. Other dimensions also indicate similar things.

It is necessary to determine the correct hole size to drill depending on thread to tap

Standard metric tapping drill sizes are as follow:

a) 3.3 mm tapping drill for M4 (x0.70mm pitch)

b) 4.2mm tapping drill for M5(x0.80mm pitch)

c) 5.0mm tapping drill for M6(x1.00 mm pitch)

d) 6.8 mm tapping drill for M8(x1.25mm pitch)

e) 8.5 mm tapping drill for M10(x1.50mm pitch)

f) 10.2 mm tapping drill for M12(x1.75mm pitch)

Steps involved in making internal thread holes using metric thread taps:

Twist the handle of wrench to widen the jaws, attach the tap using single groove to start.

Centre the drill point using a centre punch mark.

Drill a hole. The size of the hole should be lesser than size for tapping.

Apply some Rocol cutting compound on the tap’s end.

Hold the level and square to the material and twist the tap wrench until the formation of first cut into the material.

After forming a grip on the material, twist half a turn into the material and then turn it back a quarter to ensure that tap does not get jammed with residue and to get a better thread.

Keep on twisting all the way through the material and thread. There should not be any resistance on completion of the cutting through the material while revolving in or out using the tap wrench.

After completion of the process using a tap, repeat the same process using 2 grooves with the same tap, and finally, repeat the process with only tap and no groove.

At last check the threading using a bolt of appropriate size.

Relationship between metric thread taps and metric thread gauges

Technicians check the conditions of screw threads using metric thread gauges. Time to time it is necessary to check their conditions to avoid any accidents. Similar to the taps, metric gauges also come in different sizes to measure different sizes of threads. World- wide people use the ISO certified gauge for inspection and calibration of screw threads.

There are different types of metric gauges, namely metric thread plug gauge with taper lock design, metric thread plug gauge with a reversible design, metric thread ring gauge, metric set plug gauge, and southern style thread ring gauge. Though there are different purposes for both the tools- one for making holes and one for checking the conditions of the metric thread taps – both of them are essential for any manufacturing plant.


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