Recommended Hole Sizes

Pins and Dowels

It is important to follow the hole diameter instructions given by the various manufacturers and standards organisations, and the data given below comes from these sources.  However, the user should decide, in the circumstances of a particular application, which hole size, within the permitted tolerance range, to adopt, since this can effect the performance of the pin considerably.

The general principle is that the inserting pin or dowel requires significantly more force at the bottom of the hole tolerance range than at the top.  This has the following implications;-

  • The higher insertion force require, the more difficult the assembly operation, and risk of damaging or over-stressing the area of the material surrounding the hole
  • The harder the pin is to insert, the more firmly it will stay in place so in applications where vibration is a consideration, it may be worthwhile to use a minimum hole size

Recommended Hole Sizes for Spring Pins and Grooved Pins (figures in mm)

 

Diameter

Coiled Pins

(all duties)

Slotted Spring Pins

(heavy or light duty)

Groove Pins

 

MIN

MAX

MIN

MAX

MIN

MAX

0.8

0.8

0.84

-

-

-

-

1

1.00

1.04

1.00

1.10

1.000

1.025

1.2

1.20

1.24

-

-

1.200

1.225

1.5

1.50

1.60

1.50

1.60

1.500

1.525

2

1.99

2.10

2.00

2.10

2.000

2.025

2.5

2.49

2.60

2.50

2.60

2.500

2.525

3

2.99

3.10

3.00

3.10

3.000

3.025

3.5

3.48

3.62

3.50

3.62

-

-

4

3.98

4.12

4.00

4.12

4.000

4.075

4.5

-

-

4.50

4.62

-

-

5

4.95

5.12

5.00

5.12

5.000

5.075

6

5.95

6.13

6.00

6.12

6.000

6.075

7

-

-

7.00

7.12

-

-

8

7.93

8.17

8.00

8.15

8.000

8.090

10

9.93

10.20

10.00

10.15

10.000

10.090

11

-

-

11.00

11.15

-

-

12

11.90

12.22

12.00

12.17

12.000

12.110

13

-

-

13.00

13.17

-

-

14

-

-

14.00

14.17

-

-

15

-

-

15.00

15.17

-

-

16

15.85

16.25

16.00

16.17

16.000

16.110

18

-

-

18.00

18.17

-

-

20

19.85

20.25

20.00

20.17

-

-

 

Recommended Hole Sizes for Dowels

Where an interference fit is required (as opposed to a sliding or clearance fit) the dowel must be precision ground and the hole must be reamed.

The relationship between the diameter of the pin and the diameter of the hole must take into account the ductility of the dowel and the hole material and will vary more accordingly to this factor than according to the size of the dowel itself.

In hardened steel parts, the hole should be .005 to .008mm (5-8 microns) smaller than the dowel.  In unhardened material, the hole should be 0.025mm (25 microns) smaller than the dowel.

For dowels ground to m6 tolerance (Technifast standard type), the dowel diameters are as follows, and holes should be reamed to 25 microns smaller (of 5-8 microns for hardened steel) using the lower limit of the m6 range as the reference point;

 

Nominal Diameter

Dowel Diameter (m6)

0.8

0.802-0.808

1

1.002-1.008

1.5

1.502-1.508

2

2.002-2.008

2.5

2.502-2.508

3

3.002-3.008

4

4.004-4.012

5

5.004-5.012

6

6.004-6.012

8

8.006-8.015

10

10.006-10.015

12

12.007-12.018

14

14.007-14.018

16

16.007-16.018

20

20.008-20.021