Torsional Holding Power

The primary function of a rigid shaft coupling is to join two shafts such that they will function as one, retaining both the linear and angular relationship between the two shafts.

The amount of torsional load (inch-pounds or newton-meters) required to initiate slippage of a properly installed coupling is defined as the Torsional Holding Power (or Torque Rating). Since this result is a function of tension induced by the screws, the diameter of the shaft as well as the coefficient of friction between the coupling and shaft, it can be affected by many variables (smoothness of the friction surfaces, plating or lubrication on shafts or screws, size of screws and wrenching torque applied).

The amount of axial load required to initiate slippage is equal to or greater than that shown for a clamping collar of the same size. (See Axial Holding Power - clamp collars)

Because there are so many variables involved in determining the actual torsional holding power between a specific coupling and shaft, it is not possible for Stafford to certify a single value for all situations. Instead, we can provide results that have been obtained from testing under a controlled set of conditions that most accurately represent a standard operating environment. These results should be used as a guide only for projected shaft coupling performance, and should not, under any circumstances, be used as guaranteed values. The user must determine the product suitability in a particular application. The results shown were obtained in tests where there was no axial load on the coupling. Since the clamping power is providing hold against both axial and angular displacement, in applications where there is a significant axial load, the torsional holding power will be reduced.

It should be noted that in couplings with keyways, the strength of the key is the determining factor and will in most cases dramatically increase the torsional holding power.

For additional information about torsional holding power, how it is measured, or how to select the correct part for a specific application, contact us directly.

TORSIONAL HOLDING POWER

Steel Couplings Without Keyways - Inch Sizes

Alloy Socket Head
Cap Screws
Maximum Screw Torque (in-lbs)

Coupling ID
Torsional Holding Power (in-lbs)
4-40
12
1/4"
50
6-32
23
3/8"
120
8-32
41
1/2"
288
10-32
60
5/8"
480
1/4-28
168
1"
1500
1/4-28
168
1-1/2"
2256
5/16-24
324
2"
4824
3/8-24
588
2-1/4"
7905
1/2-20
1440
2-1/2"
9204

TORSIONAL HOLDING POWER

Steel Couplings without Keyways - Metric Sizes

Alloy Socket Head
Cap Screws
Maximum Screw Torque (Nm)

Coupling ID
Torsional Holding Power (Nm)
M3
1.8
8MM
4
M4
4.3
12MM
35
M5
8.7
16MM
71
M6
14.8
25MM
142
M8
35.9
50MM
456