Guidelines for Threaded Holes in CNC Machining

How to incorporate threads on your part at Protolabs

 

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
Metric
Metric Thread Guidelines arrow_right_alt
UNC
UNC Thread Guidelines arrow_right_alt
UNF
UNF Thread Guidelines arrow_right_alt

Threaded Hole Guidelines - Metric

 

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Thread Pitch Max Thread depth (mm) CAD Ø (mm) Eligible Ø (mm)
MIN MAX
M1.6 x 0.35
soft metals only		 3.00 1.25 1.22 1.32

M2 x0.4

 5.08 1.60 1.57 1.68

M2.5 x 0.45

 5.08 2.05 2.01 2.14

M3 x 0.5

 7.62 2.50 2.46 2.60

M3.5 x 0.6

 10.16 2.90 2.85 3.01

M4 x 0.7

 10.16 3.30 3.24 3.42

M5 x 0.8

 15.24 4.20 4.14 4.33

M6 x 1.0

 16.51 5.00 4.92 5.15

M8 x 1.25

 16.51 6.80 6.65 6.91

M10 x 1.5

 25.40 8.50 8.38 8.68

M12 x 1.75

 25.40 10.20 10.00 10.44

M8 x 1.0 FINE
soft metals only

 16.51 7.00 6.91 7.16

M10 x 1.25 FINE
soft metals only

 25.40 8.75 8.65 8.91

M12 x 1.25 FINE
soft metals only

 25.40 10.75 10.65 10.91

 

Thread Pitch Max Thread depth (mm) CAD Ø (mm) Eligible Ø (mm)
MIN MAX

M3 x 0.5

 7.62 2.50 2.46 2.60

M3.5 x 0.6

 10.16 2.90 2.85 3.01

M4 x 0.7

 10.16 3.30 3.24 3.42

M5 x 0.8

 10.16 4.20 4.14 4.33

M6 x 1.0
on-axis only

 12.27 5.00 4.92 5.15

M8 x 1.25
on-axis only

 12.27 6.80 6.65 6.91

M8 x 1.0 FINE
on-axis only

 16.51 7.00 6.91 7.16

M10 x 1.25 FINE
on-axis only

 25.40 8.75 8.65 8.91

 

Thread Pitch Max Thread depth (mm) CAD Ø (mm) Eligible Ø (mm)
MIN MAX 

M3.5 x 0.6

 7 3.5 3.35 3.53

M4 x 0.7

 8 4 3.84 4.03

M5 x 0.8

 10 5 4.83 5.03

M6 x 1.0

 12 6 5.79 6.02

M8 x 1.25

 16 8 7.76 8.03

M10 x 1.5

 20 10 9.73 10.03

M12 x 1.75

 24 12 11.7 12.02

M14 x 2.0

 28 14 13.68 14.03

M16 x 2.0

 32 16 15.68 16.02

M20 x 2.5

 40 20 19.62 20.03

M8 x 1.0 FINE

 16 8 7.8 8.03

M10 x 0.75 SP

 20 10 9.84 10.03

M10 x 1.25 FINE

 20 10 9.76 10.03

M12 x 1.25 FINE

 24 12 11.76 12.02

M12 x 1.0 SP

 24 12 11.79 12.02

M12 x 1.5 SP

 24 12 11.73 12.02

M14 x 1.5 FINE

 28 14 13.73 14.03

M15 x 1.0 SP

 30 15 14.79 15.03

M16 x 1.5 FINE

 32 16 15.73 16.02

M17 x 1.0 SP

 34 17 16.79 17.03

M18 x 1.5 FINE

 36 18 17.73 18.03

M20 x 1.5 FINE

 40 20 19.73 20.03

 


Coil inserts are not supplied, as standard.  Insert marked with ✓can be fitted upon request, using the special instructions textbox. They are available with a thread length of 1 × D (thread diameter), 1.5 x D and 2 x D.


Thread Pitch Max Thread depth (mm) CAD Ø (mm) Eligible Ø (mm)
MIN MAX 
✓M2 x 0.4 5.08 2.14 2.09 2.14
✓M2.5 x 0.45 7.62 2.6 2.55 2.65
✓M3 x 0.5 10.16 3.18 3.11 3.25
M3.5 X 0.6 15.24 3.7 36.8 3.79
✓M4 x 0.7 15.24 4.24 4.15 4.33
✓M5 x 0.8 16.51 5.27 5.17 5.37
✓M6 x 1.0 16.51 6.31 6.22 6.41
✓M8 x 1.25 25.4 8.38 8.27 8.48
✓M10 x 1.5 30.48 10.56 10.33 10.56
✓M12 x 1.75 30.48 12.51 12.38 12.64

 


Coil inserts are not supplied, as standard.  Insert marked with ✓can be fitted upon request, using the special instructions textbox. They are available with a thread length of 1 × D (thread diameter), 1.5 x D and 2 x D.


Thread Pitch Max Thread depth (mm) CAD Ø (mm) Eligible Ø (mm)
MIN MAX 
✓M2.5 x 0.45 7.62 2.6 2.55 2.65
✓M3 x 0.5 10.16 3.18 3.11 3.25
M3.5 x 0.6 10.16 3.7 3.68 3.79
✓M4 x 0.7 10.16 4.24 4.15 4.33
✓M5 x 0.8 10.16 5.27 5.17 5.37
✓M6 x 1.0 
on-axis only		 12.7 6.31 6.22 6.41
✓M8 x 1.25
on-axis only		 12.7 8.38 8.27 8.48

 

Threaded Holes - UNC

 

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Thread Pitch Max Thread depth (in) CAD Ø  (in) Eligible Ø (in)
MIN MAX 
#2-56 0.20 0.070 0.067 0.074
#3-48 0.20 0.082 0.076 0.084
#4-40 0.30 0.089 0.085 0.094
#5-40 0.30 0.102 0.098 0.104
#6-32 0.40 0.109 0.105 0.114
#8-32 0.40 0.135 0.130 0.139
#10-24 0.60 0.151 0.145 0.156
#12-24 0.6 0.176 0.171 0.181
1/4-20 0.65 0.202 0.196 0.207
5/16-18 0.65 0.259 0.252 0.265
3/8-16 1.00 0.314 0.307 0.321
7/16-14 1.00 0.372 0.360 0.376
1/2-13 1.00 0.426 0.417 0.434

 


Thread Pitch Max Thread depth (in) CAD Ø (in)  Eligible Ø (in)
MIN MAX 
#4-40 0.30 0.089 0.085 0.094
#5-40 0.30 0.102 0.098 0.104
#6-32 0.40 0.109 0.105 0.114
#8-32 0.40 0.135 0.130 0.139
#12-24
on-axis only		 0.5 0.176 0.171 0.181
1/4-20
on-axis only		 0.5 0.202 0.196 0.207

 

Thread Pitch Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX 
#4-40 0.22 0.112 0.106 0.113
#5-40 0.25 0.125 0.119 0.126
#6-32 0.28 0.138 0.131 0.139
#8-32 0.33 0.164 0.157 0.165
#10-24 0.38 0.190 0.182 0.191
#12-24 0.43 0.216 0.208 0.217
1/4-20 0.50 0.250 0.241 0.251

5/16-18

 0.63 0.313 0.303 0.314
3/8-16 0.75 0.375 0.364 0.376
7/16-14 0.88 0.438 0.426 0.439
1/2-13 1.00 0.500 0.488 0.501
5/8-11 1.25 0.625 0.611 0.626
3/4-10 1.50 0.750 0.735 0.751

 

Thread Pitch

 

 Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX
#2-56 0.30 0.091 0.090 0.096
#3-48 0.40 0.107 0.105 0.110
#4-40 0.40 0.119 0.117 0.125
#5-40 0.40 0.132

0.131

 0.137

#6-32

 0.60 0.147 0.145 0.153

#8-32

 0.60 0.173 0.171 0.178
#10-24 0.65 0.201 0.199 0.208
#12-24 0.65 0.227 0.225 0.234
1/4-20 0.65 0.266 0.261 0.270
5/16-18 1.00 0.332 0.324 0.334
3/8-16 1.20 0.397 0.389 0.399

7/16-14

 1.20 0.453 0.453 0.464
1/2-13 1.20 0.531 0.515 0.531
Thread Pitch

 

 Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX
#2-56 0.30 0.091 0.090 0.096
#3-48 0.40 0.107 0.105 0.110
#4-40 0.40 0.119 0.117 0.125
#5-40 0.40 0.132

0.131

 0.137

#6-32

 0.60 0.147 0.145 0.153

#8-32

 0.60 0.173 0.171 0.178
#10-24
on-axis only		 0.65 0.201 0.199 0.208
#12-24
on-axis only		 0.65 0.227 0.225 0.234

1/4-20
on-axis only

 0.65 0.266 0.261 0.270
Thread Pitch

 

 Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX 
#8-32 0.400 0.135 0.133 0.137
5/16-18 0.650 0.274 0.271 0.276
3/8-16 1.000 0.334 0.331 0.336
7/16-14 1.000 0.399 0.396 0.401
1/2-13 1.000 0.455 0.452 0.457

 

Threaded Holes - UNF

 

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Thread Pitch Max Thread depth (in) CAD Ø  (in) Eligible Ø (in)
MIN MAX 
#2-64 0.20 0.072 0.069 0.075
#3-56 0.20 0.083 0.080 0.084
#4-48 0.30 0.093 0.087 0.099
#5-44 0.30 0.104 0.100 0.104
#6-40 0.40 0.115 0.111 0.119
#8-36 0.40 0.138 0.134 0.142
#10-32 0.60 0.160 0.156 0.164
#12-28 0.6 0.182 0.177 0.186
1/4-28 0.65 0.216 0.211 0.220
5/16-24 0.65 0.272 0.267 0.277
3/8-24 1 0.335 0.330 0.340
7/16-20 1 0.389 0.383 0.395
1/2-20 1.2 0.452 0.446 0.457

Thread Pitch Max Thread depth (in) CAD Ø  (in) Eligible Ø (in)
MIN MAX 
#4-48 0.30 0.093 0.087 0.099
#5-44 0.30 0.104 0.100 0.104
#6-40 0.40 0.115 0.111 0.119
#8-36 0.40 0.138 0.134 0.142
#10-32 0.60 0.160 0.156 0.164
#12-28
on-axis only		 0.50 0.182 0.177 0.186
1/4-28
on-axis only		 0.65 0.216 0.211 0.220
5/16-24
on-axis only		 0.50 0.272 0.267 0.277
3/8-24
on-axis only		 0.50 0.335 0.330 0.340
7/16-20
on-axis only		 0.50 0.389 0.383 0.395
1/2-20
on-axis only		 0.50 0.452 0.446 0.457
Thread Pitch Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX 

#5-44

 0.250 0.125 0.12 0.126
#6-40 0.280 0.138 0.132 0.139
#8-36 0.330 0.164 0.158 0.165
#10-32 0.380 0.190 0.183 0.191
#12-28 0.430 0.216 0.209 0.217
1/4-28 0.500 0.250 0.243 0.251
5/16-24 0.630 0.313 0.304 0.314
3/8-24 0.750 0.375 0.367 0.376

7/16-20

 0.880 0.438 0.428 0.439

1/2-20

 1.000 0.500 0.491 0.501
5/8-18 1.250 0.625 0.615 0.626
3/4-16 1.500 0.750 0.739 0.751

 

Thread Pitch Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX

#2-64

 0.30 0.093 0.089 0.095

#3-56

 0.30 0.104 0.102 0.104
#4-48 0.40 0.120 0.116 0.123
#6-40 0.60 0.147 0.144 0.150
#8-36 0.60 0.173 0.170 0.177
#10-32 0.65 0.201 0.196 0.204
1/4-28 0.65 0.261 0.257 0.265
5/16-24 1.00 0.325 0.321 0.329
3/8-24 1.00 0.388 0.384 0.391
7/16-20 1.00 0.452 0.448 0.456
1/2-13 1.00 0.426 0.417 0.434
 
Thread Pitch Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX 
#2-64 0.30 0.093 0.089 0.095

#3-56

 0.30 0.104 0.102 0.104

#4-48

 0.40 0.120 0.116 0.123

#6-40

 0.60 0.147 0.144 0.150
#8-36 0.60 0.173 0.170 0.177
#10-32 0.65 0.201 0.196 0.204
1/4-28 0.65 0.261 0.257 0.265
5/16-24 1.00 0.325 0.321 0.329

3/8-24

 1.00 0.388 0.384 0.391

7/16-20

 1.00 0.452 0.448 0.456
1/2-13 1.00 0.426 0.417 0.434
Thread Pitch Max Thread depth (in) CAD Ø (in) Eligible Ø (in)
MIN MAX 
#10-32 0.600 0.162 0.160 0.164
#12-28 0.600 0.189 0.186 0.191
1/4-28 0.650 0.229 0.227 0.231

Maximum Threading Reach

THREADING: MAXIMUM REACH

Example 1:

This is a cross-section view of a through hole that is threaded from one side. In this case, the hole depth exceeds the reach of the tool. The result is an unthreaded section that is opposite the side selected.

Example 2:

This is a cross-section view of a through hole that is threaded from one side. In this case, the hole depth does not exceed the reach of the tool. The result is the threads will be formed across the entire length of the hole.

Example 3:

This is a cross-section view of a through hole that is threaded from two sides. In this case, the hole depth is too long to reach from one side only. However, it can be reached past the centre from either side. If this hole is selected to be threaded from both sides, there will be a discontinuity in the middle of the hole. This means that a bolt can only be threaded to roughly half the depth of the hole.

Example 4:

This is a cross-section view of a through hole that is threaded from both sides. This is similar to Example 3, but the hole is longer and the tool can not reach to the centre from either side. In this case, the hole will be threaded to the maximum reach from both sides, leaving an un-threaded section in the middle.

Example 5:

This is a cross-section view of a blind hole (a hole that has a bottom/doesn’t pass through the part). In this case, the hole is less than the full reach and threading will stop roughly 0.25 mm (0.010 in) off the bottom. If the hole is deeper than the tool can reach, threads will be cut as deep as possible.

Example 6:

A designer may add a point at the bottom of a blind hole. In most cases, this represents the point left if a pilot hole is drilled with a drill bit. It may also serve a function to their design, or provide an area for chips that are generated during the threading process to fall. If this point is added to the model, the threading will stop roughly 0.25 mm above the start of the point angle.