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Ground dowel Straight

Clevis Grooved

Taper Cotter

UNIT 9a: Non-threaded Fasteners

Introduction

Non-threaded fasteners are devices that have no threaded portion but are used to hold or transmit

load from one component to another in an assembly or joint. They use means like friction or

deformation or both to develop the grip that keeps components together in the joint or assembly.

Examples of non-threaded fasteners are pins, keys, retaining rings, rivets, etc. Like threaded

fasteners, some non-threaded fasteners are used to create detachable assembly, but others like

rivets produce semi-permanent joints that can be detached only when the rivets are destroyed.

Pins Pins can hold two or more components together in a detachable assembly. Some pins are used to

locate components in position while others are used to transmit relatively low values of torque.

Common pins are straight, dowel, taper, clevis, grooved and cotter types and are shown in Fig. 1.

Dimensions of pins are standardized and can be obtained from tables from different sources like

the Machinery Handbook. Pins may be specified by diameter and length.

Fig.1: Some types of pins

Keys Keys are fasteners that are used to secure a component with a hub on a shaft for torque

transmission. They are used to secure gear-wheels, pulleys, sprockets, hand-wheels, levers or

handles on shafts or axles. A keyseat is the key slot on a shaft and a keyway is the key slot on a

hub. Keyseats are most often produced by vertical or horizontal milling cutters while keyways are

produced by slotting and broaching. The sharp fillet radius at the base of a keyway or keyseat

results in high stress concentration. The joint produced by a key is detachable. The key is

assembled in the keyseat with snug or some interference by has a clearance fit with the hub. A

snug fit creates an unstrained joint while an interference fit creates a strained joint.

The primary function of a key is to transmit torque between a shaft and a hub. However, it may

be used to fix or allow axial motion on the shaft. The main advantages of a key joint are a) simple

construction, b) reliability in service, c) ease of assembly and disassembly, and d) low cost.

Disadvantages include reduced shaft strength due to stress concentration, limited power

transmission, and elaborate modifications sometimes when the hub needs to be moved on the

shaft. Keys are commonly made from plain carbon steel stocks and some national codes

recommend a minimum tensile strength for key materials.

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There are several types of keys. They are mainly distinguished by shape in the cross-section or

longitudinal direction. Popular types of keys are plain, Gib-head, taper, and woodruff. Fig. 2

shows some types of keys. A plain key may have a square or rectangular cross-section. A Gib-

head key may be of the plain or tapered key type except that it has a head portion. A taper key has

a sloping top with a gradient of 1: 100 (metric) or 1:96 (English). A woodruff key is a portion of

rod sized as a key.

(a)

(b)

(c)

(d)

(f)

(e)

Fig. 2 Types of keys

a) Square or rectangular key. b) Square or rectangular key with rounded ends.

b) Square or rectangular with gib head key. d) Tapered rectangular key. e) Tapered gib head key

f) Woodruff key.

Key dimensions in cross-section (width x thickness; bxh) are standardized and can be obtained

from tables for known shaft diameters. The width (b) of a key is roughly one-quarter of the shaft

diameter. The thickness (h) of the key is usually equal to or slightly smaller than the width. The

length of the key must then be determined based on the transmitted toque value.

Fig. 3 shows the elements of a key assembly.

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Fig. 3: Elements of a key assembly

A sunk key has a portion in the keyseat of a shaft and the remaining portion in the keyway

of a hub. Hence key slots are required on the shaft and hub. A saddle key fits into a key slot cut

only on a hub. Its mating surface with a shaft may be flat or curved (concave). It transmits power

by friction between the interface of the key and shaft. Saddle keys are limited in power

transmission because of the slipping tendency of the shaft, though it is cheaper to assemble. Sunk

keys are the most popular types of key.

A feather key is a sunk parallel key fixed on a shaft or hub and allows relative movement between

the shaft and hub. The key can be fixed by different methods but cap screws with countersunk

heads are common. Most often, the key is fixed on the shaft so that the hub can slide over it.

Feather keys are used where parts mounted on a shaft must be move axially for functional

reasons. Examples are clutches and some gear shifting devices. They are alternatives to splines.

The shaft and hub dimensions (Fig. 4) are also given in tables.

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Table 1: Key and Slot Sizes for Rectangular and Tapered Keys

Shaft Size

(mm)

Key Size Shaft Depth (mm) Hub depth (mm)

Width (mm) Depth (mm) (t1) Rectangular (t2) Tapered (t2)

6 to 8 2 2 1.2 1.0 0.5

8 to 10 3 3 1.8 1.4 0.9

10 to 12 4 4 2.5 1.8 1.2

12 to 17 5 5 3.0 2.3 1.7

17 to 22 6 6 3.5 2.8 2.2

22 to 30 8 7 4.0 3.3 2.4

30 to 38 10 8 5.0 3.3 2.4

38 to 44 12 8 5.0 3.3 2.4

44 to 50 14 9 5.5 3.8 2.9

50 to 58 16 10 6.0 4.3 3.4

58 to 65 18 11 7.0 4.4 3.4

65 to 75 20 12 7.5 4.9 3.9

75 to 85 22 14 9.0 5.4 4.4

85 to 95 25 14 9.0 5.4 4.4

95 to 110 28 16 10.0 6.4 5.4

110 to 130 32 18 11.0 7.4 6.4

130 to 150 36 20 12.0 8.4 7.1

150 to170 40 22 13.0 9.4 8.1

170 to 200 45 25 15.0 10.4 9.1

200 to 230 25 28 17.0 11.4 -

230 to 260 56 32 20.0 12.4 -

260 to 290 63 32 20.0 12.4 -

290 to 330 70 36 22.0 14.4 -

330 to 380 80 40 25.0 15.4 -

380 to 440 90 45 28.0 17.4 -

440 to 500 100 50 31.0 19.5 -

Standard key length (mm)

6, 8, 10, 12, 14, 16, 18, 20, 22, 25, 28, 32, 36, 40, 45, 50, 55, 60, 65, 70, 80, 90, 100, 110, 125,

140, 160, 180, 200, 220, 250, 280, 320, 360, 400

Table 2: Fillet and Chamfer Sizes for Rectangular and Tapered Keys

Shaft Size (mm) Fillet Radius Chamfer

Max. (mm) Min. (mm) Min (mm) Max. (mm)

6 to 12 0.16 0.08 0.16 0.25

12 to 30 0.25 0.16 0.25 0.40

30 to 65 0.40 0.25 0.40 0.60

65 to 130 0.60 0.40 0.60 0.80

130 to 230 1.00 0.70 1.00 1.20

230 to 330 1.60 1.20 1.60 2.00

330 to 500 2.50 2.00 2.50 3.00

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U.S. Woodruff Keys

Key Size (mm) Shaft Depth (mm) Hub Depth (mm) Offset (mm)

bxhxD t1 t2 e

1.5x3x6 1.8 0.95 0.4

1.5x4x10 3.4 0.95 0.4

2x4x10 3.0 1.3 0.4

2x5x12 3.8 1.3 1.0

2x6x16 5.0 1.3 1.5

3x5x12 3.4 1.7 1.0

3x6x16 4.6 1.7 1.5

3x8x20 6.2 1.7 1.5

5x6x16 4.2 2.1 1.5

5x8x20 5.8 2.1 1.5

5x10x22 7.4 2.1 1.5

5x8x20 5.4 2.5 1.5

5x10x22 7.0 2.5 1.5

5x11x25 8.6 2.5 1.5

6x10x22 6.2 3.3 1.5

6x11x25 7.8 3.3 1.5

6x14x30 10.6 3.3 2.0

8x11x25 7.0 4.1 1.5

8x14x30 9.8 4.1 2.0

8x16x38 12.2 4.1 3.0

10x14x30 9.0 4.9 2.0

10x16x38 11.4 4.9 3.0

Woodruff Keys (Metric)

Key Size (mm) Shaft Depth

(mm)

Hub Depth

(mm) Fillet Radius (mm)

Chamfer (mm)

bxhxD t1 t2 Max. Min. Min. Max.

1.0 x 1.4 x 4 1.0 0.6

0.16 0.08 0.16 0.25

1.5 x 2.6 x 7 2.0 0.8

2.0 x 2.6 x 7 1.8 1.0

2.0 x 3.7 x 10 2.9 1.0

2.5 x 3.7 x 10 2.7 1.2

3.0 x 5.0 x 13 3.8 1.4

3.0 x 6.5 x 16 5.3 1.4

4.0 x 6.5 x 16 5.0 1.8

0.25 0.16 0.25 0.40

4.0 x 7.5 x 19 6.0 1.8

5.0 x 6.5 x 16 4.5 2.3

5.0 x 7.5 x 19 5.5 2.3

5.0 x 9.0 x 22 7.0 2.3

6.0 x 9.0 x 22 6.5 2.8

6.0 x 11.0 x 28 7.5 2.8

8.0 x 11.0 x 28 8.0 3.3 0.40 0.25 0.40 0.60

10.0 x 13.0 x 32 10.0 3.3

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Fig. 4: Hub and shaft key dimensions

Splines

Splines may be considered as multiple keys made as integral parts of shaft. The hub on the other

member has grooves that match the spline shape on the shaft. The shaft has multiple external keys

while the hub has matching multiple internal keyways. Splines can transmit large values of torque

and are resistant to shock, vibration and fatigue. They are standardized and are available in

rectangular or involute section styles and provide one of the strongest methods of transmitting

torque. The teeth of rectangular splines have straight sides while involute splines have teeth with

involute profile. The involute spline is preferred to rectangular spline because it provides for self-

locking [Mott, p. 503] of the mating teeth and it can be machined with standard hobs on gear

cutting machines. The common involute profile has 30o pressure angle. Involute splines are easier

to manufacture with high accuracy and often need no grinding. They are less susceptible to stress

concentration compared with rectangular splines. Splines are machined accurately to provide a

controlled fit between mating teeth of the external keys and internal keyways. Rectangular splines

can be side-fitted, major-diameter fitted, or minor-diameter fitted [Petrov, p. 346]. In side-fitted

rectangular splines, the fit is controlled by varying the thickness of the teeth. This method is not

as accurate as the major- or minor-diameter method but is preferred for heavy-duty joints

intended for large torque transmission and suddenly applied loads. In major-diameter fitted

rectangular splines, the fit is controlled by varying the major diameter of the spline on the shaft

and offers the best accuracy. In minor-diameter fitted rectangular splines, the fit is controlled by

varying the minor diameter of the spline on the shaft. This method is used for hardened hubs.

Involute splines are usually fitted on the sides of the teeth for better accuracy than the major

diameter which is done less frequently. They can be used as fixed and movable joints.

Rectangular splines are used as fixed joints [Mott, p. 503]. In movable joints, the surfaces of the

splines are often hardened to improve wear resistance and facilitate axial motion. Splines come in

different sizes, and materials. The number of teeth on rectangular splines may be 4, 6, 10, or 16.

Involute splines have even number of teeth in the range of 6 to 60, and have the addendum equal

to the module and the dedendum equal to 1.35 times the module in American practice. There are

15 standard modules of 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5, 3, 4, 5, 6, 8, and 10. Fig. 5

shows the cross-section of some types of splines and assembly.

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External Internal

Retangular splines

External Internal

Involute splines

Assembly

Assembly

Rectangular Spline fitting

Major-diameter fitted Minor-diameter fitted Side fitted

Fig.5: Some types of splines

Retaining Rings Retaining rings are used to provide a stop or a shoulder for positively locating bearings or other

devices on a shaft. They are also used internally to secure a cylindrical feature in housing.

Common types of retaining rings need a groove on a shaft or housing for mounting with a special

pier. Fig. 6 shows some types of retaining rings. There are special types available.

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Basic Internal Basic External Inverted External

Inverted Internal Beveled Internal Beveled External

Fig. 6: Some types of retaining rings.