Threaded Holes Guidelines


 

Threaded Parts in 5 Easy Steps:

  1. Model holes in your CAD design using the pilot hole diameter (listed below)
  2. Upload your CAD quotation
  3. Our software will automatically show which threads are eligible
  4. On the interactive quote select the holes you need to thread (or select all)
  5. The thread depth is shown on the quote along with the price

 

Understanding thread depth:

All of our threads are CNC cut using a thread mill and manually gauged during final inspection.

Thread milling is more reliable than manual tapping, but for the best results thread depth is regulated to about 2.5 times the thread diameter (refer to maximum depth in the table below). Don’t worry if your hole is longer or shorter, here’s how our software will design your thread:

QUICK THREADS:
  • Easy: Select all of your threaded holes with a single drop down
  • Specific: Or select specific threads by clicking on the CAD model
  • Quick: No need to 2D drawings, or text explanation
  • Wide range: We offer a range of metric, metric fine, unified fine and coarse (UNF/UNC)
  • Right Handed: All threads will be right handed

Blind hole <Ø×2.5

Threaded to the end (the last thread will stop about 0.25 mm from the end or drill tip)

Blind hole >Ø×2.5

The first portion of the hole will be threaded (to a depth of about Ø×2.5 )

Through hole <Ø×2.5

Completely threaded

Through hole >Ø×2.5

If we can access both sides, the thread selection will allow selection of either or both sides. If you select both the threads will each be a little less than ½ the depth of the hole: they will not meet in the middle.

Through hole >Ø×5

For longer holes the threads will be cut to the maximum depth possible

Tip for increasing overall thread depth

Adding a counter bore will enable the thread tool to reach further. A counter bore, or countersink, is also a great Design for Assembly (DfA) feature.


Coil and key inserts

Coil inserts (HELICOIL®) and key inserts can provide a more durable thread in softer materials. We can machine insert ready threads, these can be selected using our interactive quote.

We will also supply and fit a range of standard metric HELICOIL® inserts, with a thread length of 1 × thread diameter (D), 1.5D and 2D. If you require fitted inserts, let us know by using the special instructions button on your quote; please include insert length and location information.

Other considerations:

Occasionally part features or fixturing will obstruct the thread tools, if a hole cannot be threaded we show this by omitting the thread on the interactive quotation.

For threading on turned parts simply model the nominal diameter; there is no need to model the threads.

Our standardised toolset enables incredibly quick CNC manufacturing (as quick as same day) however it also means we can only provide the threads listed, left handed threads, diameters or pitches not listed are not currently possible.

We can only support modelled threads larger than M12 or UNC ½”-13 (½” Unified Course by 13 Thread Per Inch (TPI)) or greater – they will be milled using a ball cutter.

We are unable to support .SLT file formats

What is the minimum thread depth? Our software will recognise threadable holes that have a depth of at least 1.5 x thread pitch.

What is the recommended minimum thread depth? The recommended minimum depth for a strong thread is 1 x diameter for steels and hard metals, 2 x diameter for aluminium alloys and soft metals and as deep as possible for plastics: 2.5 x Ø (a Helicoil® insert is recommended to further increase thread strength and durability in soft materials).


Internal Metric 

Thread Pitch

 

Process Max Thread depth CAD Ø * Eligible Ø Clearance Ø
MILLING TURNING MIN MAX 

Internal metric: standard or coarse - all dimensions in mm

M1.6 x 0.35** Soft**   3.00 1.25 1.22 1.32 1.65

M2 x0.4

 ✓   5.08 1.60 1.57 1.68 2.05

M2.5 x 0.45

 ✓   5.08 2.05 2.01 2.14 2.60

M3 x 0.5

7.62 2.50 2.46 2.60 3.10

M3.5 x 0.6

10.16 2.90 2.85 3.01 3.60

M4 x 0.7

10.16 3.30 3.24 3.42 4.10

M5 x 0.8

15.24 / 10.16T* 4.20 4.14 4.33 5.10

M6 x 1.0

on-axis only 16.51 / 12.27T* 5.00 4.92 5.15 6.10

M8 x 1.25

on-axis only 16.51 / 12.27T* 6.80 6.65 6.91 8.20

M10 x 1.5

  25.40 8.50 8.38 8.68 10.20

M12 x 1.75

  25.40 10.20 10.00 10.44 12.20

Internal metric: fine or special - all dimensions in mm

M8 x 1.0 FINE

Metal*** on-axis only 16.51 7.00 6.91 7.16 8.20

M10 x 1.25 FINE

Metal*** on-axis only 25.40 8.75 8.65 8.91 10.20

M12 x 1.25 FINE

Metal***   25.40 10.75 10.65 10.91 12.20

Obstruction by other features of your part, lead-in treatments, or fixturing requirements may reduce the maximum depth of threads.

* also known as - Pilot Hole Drill Ø

Soft** Only available in soft metals

Metal *** -Only available in metal materials (both hard and soft)

T* - Turned

The Minimum Ø and Maximum Ø are the limits our software uses to recognise holes that can be threaded

The maximum thread depth is the limit of our thread cutting tools, starting from the hole face selected, excluding any chamfers of counter bores. Your hole should be deeper than this depth to allow for swarf. Even if you model a deeper hole, only the first portion will be threaded.


Coil insert metric 

Coil inserts are not supplied, as standard.

We can supply and fit helicoils to all threads marked #, please request when quoting using the special instructions textbox.

 


Thread Pitch

 

Process Max Thread depth CAD Ø  Eligible Ø Clearance Ø
MILLING TURNING MIN MAX 

Internal metric: standard or coarse - all dimensions in mm

M2 x 0.4 ✓#   5.08 2.14 2.09 2.14 2.05
M2.5 x 0.45 ✓# ✓# 7.62 2.6 2.55 2.65 2.60
M3 x 0.5 ✓# ✓# 10.16 3.18 3.11 3.25 3.10
M3.5 x 0.6 15.24 / 10.16T* 3.7 3.68 3.79 3.60
M4 x 0.7 ✓# ✓# 15.24 / 10.16T* 4.24 4.15 4.33 4.10
M5 x 0.8 ✓# ✓# 16.51 / 10.16T* 5.27 5.17 5.37 5.10
M6 x 1.0 ✓# on-axis only # 16.51 / 12.7T* 6.31 6.22 6.41 6.10
M8 x 1.25 ✓# on-axis only # 25.4 / 12.7T* 8.38 8.27 8.48 8.20
M10 x 1.5 ✓#   30.48 10.56 10.33 10.56 10.20
M12 x 1.75 ✓#   30.48 12.51 12.38 12.64 12.20

* also known as Pilot Hole Drill Ø

T* - Turning

✓ = Threads are available: Outside diameter (on-axis), inside diameter: on axis, axial and radial.

# = Helicoil® thread inserts can be fitted on request, and are available with a thread length of 1 × thread diameter (D), 1.5D and 2D.


Outside diameter metric

Thread Pitch

 

Process Max Thread depth CAD Ø Eligible Ø Clearance Ø
MILLING TURNING MIN MAX 

Metric outside diameter: standard or coarse - all dimensions in mm

M3.5 x 0.6

  7 3.5 3.35 3.53 3.16

M4 x 0.7

  8 4 3.84 4.03 4.10

M5 x 0.8

  10 5 4.83 5.03 5.10

M6 x 1.0

  12 6 5.79 6.02 6.10

M8 x 1.25

  16 8 7.76 8.03 8.20

M10 x 1.5

  20 10 9.73 10.03 10.20

M12 x 1.75

M* 24 12 11.7 12.02 12.20

M14 x 2.0

M* 28 14 13.68 14.03 14.25

M16 x 2.0

M* 32 16 15.68 16.02 16.25

M20 x 2.5

M* 40 20 19.62 20.03 20.25

Metric outside diameter: fine or special - all dimensions in mm

M8 x 1.0 FINE

  16 8 7.8 8.03 8.20

M10 x 0.75 SP

  20 10 9.84 10.03 10.20

M10 x 1.25 FINE

  20 10 9.76 10.03 10.20

M12 x 1.25 FINE

  24 12 11.76 12.02 12.20

M12 x 1.0 SP

  24 12 11.79 12.02 12.20

M12 x 1.5 SP

M* 24 12 11.73 12.02 12.20

M14 x 1.5 FINE

M* 28 14 13.73 14.03 14.25

M15 x 1.0 SP

M* 30 15 14.79 15.03 15.25

M16 x 1.5 FINE

M* 32 16 15.73 16.02 16.25

M17 x 1.0 SP

M* 34 17 16.79 17.03 17.25

M18 x 1.5 FINE

M* 36 18 17.73 18.03 18.25

M20 x 1.5 FINE

M* 40 20 19.73 20.03 20.25

*also known as - Pilot Hole Drill Ø

M* On a 3 or 5-axis mill larger external threads can be cut with a ball nose cutter… refer to Special threads.


Internal Inch


Thread Pitch

 

Process Max Thread depth CAD Ø  Eligible Ø Clearance Ø
MILLING TURNING MIN MAX 

Internal inch: unified fine UNF - all dimensions in inches

#2-64   0.20 0.072 0.069 0.075 0.09
#3-56   0.20 0.083 0.080 0.084 0.10
#4-48 0.30 0.093 0.087 0.099 0.12
#5-44 0.30 0.104 0.100 0.104 0.13
#6-40 0.40 0.115 0.111 0.119 0.14
#8-36 0.40 0.138 0.134 0.142 0.17
#10-32 0.60 0.160 0.156 0.164 0.19
#12-28 on-axis only 0.6 / 0.5T* 0.182 0.177 0.186 0.22
1/4-28 on-axis only 0.65 0.216 0.211 0.220 0.26
5/16-24 on-axis only 0.65 /0.5T* 0.272 0.267 0.277 0.32
3/8-24 on-axis only 1 / 0.5T* 0.335 0.330 0.340 0.38
7/16-20 on-axis only 1 / 0.5T* 0.389 0.383 0.395 0.44
1/2-20 on-axis only 1.2 / 0.5T* 0.452 0.446 0.457 0.51

Internal inch: unified coarse UNC - all dimensions in inches

#2-56   0.20 0.070 0.067 0.074 0.09
#3-48   0.20 0.082 0.076 0.084 0.10
#4-40 0.30 0.089 0.085 0.094 0.12
#5-40 0.30 0.102 0.098 0.104 0.13
#6-32 0.40 0.109 0.105 0.114 0.14
#8-32 0.40 0.135 0.130 0.139 0.17
#10-24   0.60 0.151 0.145 0.156 0.19
#12-24 on-axis only 0.6 / 0.5T* 0.176 0.171 0.181 0.22
1/4-20 on-axis only 0.65 / 0.5T* 0.202 0.196 0.207 0.26
5/16-18   0.65 0.259 0.252 0.265 0.32
3/8-16   1.00 0.314 0.307 0.321 0.38
7/16-14   1.00 0.372 0.360 0.376 0.44
1/2-13   1.00 0.426 0.417 0.434 0.51

* also known as Pilot Hole Drill Ø

T* - Turning 


Coil Insert Inch

Coil inserts are not supplied

Thread Pitch

 

Process Max Thread depth CAD Ø Eligible Ø Clearance Ø
MILLING TURNING MIN MAX 

Inch coil insert: unified fine UNF - all dimensions in inches

#2-64

0.30 0.093 0.089 0.095 N/A

#3-56

0.30 0.104 0.102 0.104 N/A

#4-48

0.40 0.120 0.116 0.123 N/A

#6-40

0.60 0.147 0.144 0.150 N/A

#8-36

0.60 0.173 0.170 0.177 N/A

#10-32

0.65 0.201 0.196 0.204 N/A

1/4-28

on-axis only 0.65 0.261 0.257 0.265 N/A

5/16-24

on-axis only 1.00 0.325 0.321 0.329 N/A

3/8-24

on-axis only 1.00 0.388 0.384 0.391 N/A

#7/16-20

on-axis only 1.00 0.452 0.448 0.456 N/A

1/2-13

on-axis only 1.00 0.426 0.417 0.434 N/A

Inch coil insert: unified coarse UNC - all dimensions in inches

#2-56

0.30 0.091 0.090 0.096 N/A

#3-48

0.40 0.107 0.105 0.110 N/A

#4-40

0.40 0.119 0.117 0.125 N/A

#5-40

0.40 0.132

0.131

0.137 N/A

#6-32

0.60 0.147 0.145 0.153 N/A

#8-32

0.60 0.173 0.171 0.178 N/A

#10-24

on-axis only 0.65 0.201 0.199 0.208 N/A

#12-24

on-axis only 0.65 0.227 0.225 0.234 N/A

1/4-20

on-axis only 0.65 0.266 0.261 0.270 N/A

5/16-18

  1.00 0.332 0.324 0.334 N/A

3/8-16

  1.20 0.397 0.389 0.399 N/A

7/16-14

  1.20 0.453 0.453 0.464 N/A

1/2-13

  1.20 0.531 0.515 0.531 N/A

* * also known as - Pilot Hole Drill Ø


Key Insert Inch

Key inserts are not supplied

Thread Pitch

 

Process Max Thread depth CAD Ø Eligible Ø Clearance Ø
MILLING TURNING MIN MAX 

Inch key insert: Unified fine UNF - all dimensions in inches

#10-32

  0.600 0.162 0.160 0.164 N/A

#12-28

  0.600 0.189 0.186 0.191 N/A

1/4-28

  0.650 0.229 0.227 0.231 N/A

Inch key insert: Unified coarse UNC - all dimensions in inches

#8-32

  0.400 0.135 0.133 0.137 N/A

5/16-18

  0.650 0.274 0.271 0.276 N/A

3/8-16

  1.000 0.334 0.331 0.336 N/A

7/16-14

  1.000 0.399 0.396 0.401 N/A

1/2-13

  1.000 0.455 0.452 0.457 N/A

* * also known as - Pilot Hole Drill Ø


Outside diameter inch

Thread Pitch

 

Process Max Thread depth CAD Ø Eligible Ø Clearance Ø
MILLING TURNING MIN MAX 

Inch outside diameter: unified fine UNF - all dimensions in inches

#5-44

  0.250 0.125 0.12 0.126 0.13

#6-40

  0.280 0.138 0.132 0.139 0.14

#8-36

  0.330 0.164 0.158 0.165 0.17

#10-32

  0.380 0.190 0.183 0.191 0.19

#12-28

  0.430 0.216 0.209 0.217 0.22

1/4-28

  0.500 0.250 0.243 0.251 0.26

5/16-24

  0.630 0.313 0.304 0.314 0.32

3/8-24

  0.750 0.375 0.367 0.376 0.38

7/16-20

  0.880 0.438 0.428 0.439 0.44

1/2-20

M* 1.000 0.500 0.491 0.501 0.51

5/8-18

M* 1.250 0.625 0.615 0.626 0.64

3/4-16

M* 1.500 0.750 0.739 0.751 0.76

Inch outside diameter: fine or special - all dimensions in inches

#4-40

  0.22 0.112 0.106 0.113 0.12

#5-40

  0.25 0.125 0.119 0.126 0.13

#6-32

  0.28 0.138 0.131 0.139 0.14

#8-32

  0.33 0.164 0.157 0.165 0.17

#10-24

  0.38 0.190 0.182 0.191 0.19

#12-24

  0.43 0.216 0.208 0.217 0.22

1/4-20

  0.50 0.250 0.241 0.251 0.26

5/16-18

  0.63 0.313 0.303 0.314 0.32

3/8-16

  0.75 0.375 0.364 0.376 0.38

7/16-14

  0.88 0.438 0.426 0.439 0.44

1/2-13

M* 1.00 0.500 0.488 0.501 0.51

5/8-11

M* 1.25 0.625 0.611 0.626 0.64

3/4-10

M* 1.50 0.750 0.735 0.751 0.76

*also known as - Pilot Hole Drill Ø

M* On a 3 or 5-axis mill larger external threads can be cut with a ball nose cutter… refer to Special threads.

Outside diameter special threads

External threads can be milled, this normally only works well for larger threads, as these will be milled using a ball end cutter (M4 is the absolute minimum, but ideally M12 and above). Your thread will have radii in the root, so might need cleaning up with a die. We can mill most custom threads or helical forms that you can model – on the lathe, 5-axis mill or 3-axis. External 3-axis milled threads are produced on the half diameter. The part is then rotated 180 degrees, re-referenced, and the other half milled.

On parts that require externally milled threads, you must design the threads on your part. We manufacture your design using flat and ball end mills. It is not the preferred method for producing threads, but can be useful for producing ¼ turn fasteners or helical and camming features.

The CAD file should then be submitted in a 3D file format other than STL; we accept most native CAD formats or a standard file formats such as IGES or STEP are also great.
Note: for standard threads only model the drill or outside diameter, we are unable to manufacture standard threads that have been modelled.