View Full Version : Summary: max. torque with a screwdriver

05-06-1998, 01:45 AM
Thanks to everybody who replied to my question.
To summarize:
- Order of magnitude = 5 to 10 Nm
- Biblio refs = many in the ergonomy field plus the NASA Anthropometric
source book
- But most important ... it is a wrong question because it depends by many
factors (one for all the handle). As usual below are reported all the

thanks again


ps: I left the reply of Paolo de Leva in Italian so you can practice with
our beautiful language

**************ORGINAL REQUEST*******************
Dear All,
we are testing a two part device. The two parts are connected with a screw
which should be tightened by the surgeon with a screwdriver.

Does anybody knows what is the max. torque an average man can produce with
a screwdriver? A biblio reference to be cited would be great. My medline
search was inconcludent; I guess I am not using the right keywords .......


From: Geo4PL

We've done some testing here and found that around 60 to 70 in-lbs is
typical but that depends on your screw/tool interface.

George Iwanski
From: Jean-Francois.Benvenuti@epfl.ch

You should ask a car mecanician. They have tables of such data. Bye.

Benvenuti Jean-Francois
Laboratoire de Genie Medical
Swiss Federal Institute of Technology of Lausanne PSE-EPFL
CH-1015 Lausanne Switzerland.
tel: ++41 21 693 83 38
fax: ++41 21 693 83 30
From: Dann L Chow


You might be able to find something if you look in ergonomics journals
instead of medical ones...actually, let me have a quick look for you...OK,
here's one:

D.J. Habes and K.A. Grant
EMG study of maximum torques and upper extremity muscle activity in
simulated screwdriving tasks
International Journal of Industrial Ergonomics v20 n4 Oct 1997, p339-346
I don't have the article, but good luck finding it. DC
Sender: small@me.queensu.ca

Dear Marco,
How big is the handle? That will clearly be the limiting factor in
generating torque. My guess is that you will want to limit, rather than
augment, whatever forces are applied manually (speaking as a female who can
strip aluminum screw threads on her bicycle without breaking a sweat).
Hence the invention of the torque-wrench.


************************************************** *************
Carolyn F. Small, PhD, PEng
Professor, (613)545-2581
Department of Mechanical Engineering FAX 545-6489
Queen's University
Kingston, Ontario, Canada
K7L 3N6 small@me.queensu.ca
************************************************** *************
From: "Karl Kraus" Reply-To:

As you might guess, there is quite a bit of variability not only between
surgeons, but with different screw driver handles. We conducted a study of
ten surgeons using a screw driver type wrench and an open ended wrench with
a 15cm handle. The mean with the screw driver was 4.4 Nm and 7.8 with the
open ended wrench. (Kraus et al, Vet surg., 1998)
From: Andrew_Pinder@hsl.gov.uk

Maximum torque will depend on a lot of factors: Handle diameter,
orientation, arm posture, surface roughness etc. A better question is how
can this device be designed so that the surgeon can tighten the screw with
only a small amount of force?
Stephen Pheasant discussed the issue of screwdriver design and torque in
his book:
Bodyspace: Anthropometry, Ergonomics and the Design of Work, 2nd Edition,
Taylor & Francis, London, 1996.
He also referred to two earlier papers:
Pheasant ST and O'Neill D (1975) "Performance in gripping and turning",
Applied Ergonomics, 6, 205-208.
Pheasant ST and Scriven JG (1983) "Sex differences in strength - some
implications for the design of hand tools". Proceedings of the Ergonomics
Society Conference 1983, ed. K Coombes, Taylor & Francis, London, pp 9-13.

Ergonomics and Work Psychology Section
Health and Safety Laboratory, Broad Lane, Sheffield, S3 7HQ, UK Tel +44 114
289 2594; Fax +44 114 289 2526 HSE home page:
http://www.open.gov.uk/hse/hsehome.htm -

From: "Eric Powell"

Why not try to find out for yourself? You could weld a nut socket to the
end of a screwdriver. Then attach this to a torque wrench used for car
maintenance, hold the wrench in a vice, and get your volunteers to try and
turn the torque wrench.


Dr Eric Powell
Research Bioengineer
Rehabilitation Research
Phase 2
Hope Hospital
Eccles Old Road
Salford M6 8HD
United Kingdom
telephone: (44) 0161 787 1128
(e-mail epowell@fs1.ho.man.ac.uk)
From: "Kazakia, Galateia"

Dr. Viceconti,
I have recently been addressing this question myself. It seems that some of
the best data comes not from the orthopaedic field, but from US Government
sponsored studies meant to aid in the design of air and space craft
A report available from the Center for Aerospace Information of the
National Aeronautics and Space Administration (NASA) entitled
"Anthropometric Source Book" (NASA RP-1024) is a compilation of a large
amount of anthropometric data aimed to meet the needs of engineers
designing clothing, equipment, and workspaces for the NASA Space Shuttle
Program. This information is, of course, very useful for engineers in a
variety of fields. Volume I contains a chapter entitled "Human Muscular
Strength". It contains much strength information including data on volar
flexion/dorsal extension and supination/pronation strength for both men and
women. The most relevant references from this chapter seem to be:

1. Asmussen E, and Heeboll-Nielsen K, 1961. "Isometric Muscle Strength of
Adult Men and Women, " Communications from the Testing and Observation
Institute of the Danish National Association for Infantile Paralysis, 11:

2. Backlund L, and Nordgren L, 1968. "A New Method for Testing Isometric
Muscle Strength Under Standardized Conditions," Scandinavian J. of Clinical
and Laboratory Investigation, 21(1): 33-41.

3. Lauback LL, 1976. "Comparative Muscular Strength of Men and Women: A
Review of the Literature," Aviation, Space, and Environmental Medicine,
47(5): 534-542.

4. Lauback LL, 1976. Muscular Strength of Women and Men: A Comparative
Study. AMRL-TR-75-32, Aerospace Medical Research Laboratories,
Wright-Patterson Air Force Base, Ohio.

This report (NASA RP-1024) and others can be found (and ordered?) on the
following page:


I hope this is helpful!

Galateia Kazakia
Design Engineer
The Hospital for Special Surgery

phone: 212.606.1434
fax: 212.794.4020
email: kazakiag@hss.edu

From: "w.p. mossel"

The question is wrong. Because it depends on the diameter of the grip of
the srewdriver. I am not a surgeon and I don't know with what kind of
screwdrivers surgeons work. For instance when the handle has a T-form the
torque can be larger than with a handle with a small cilinder form . I am
now at home and not in the university. I thought I had some values about
the torque of human hands. On monday I'll be in the university and will
mail you what I have about torque.
"All spelling errors due to line noise"
Kind regards, Vriendelijke groet, Grusze Wim Mossel

a.k.a. w.p.mossel@io.tudelft.nl
Phone: +31 15 278 35 64, Fax: +31 15 278 71 79 Address : Jaffalaan 9
2628 BX Delft
The NetherlandsDate: Fri, 01 May 1998 11:55:36 -0400
From: Kevin Bender

Try the following references:

Mital & Channaveeraiah. "Peak volitional torques for wrenches and
(1988), 41-64.

Shih & Wang. "Hand/tool interface effects on human torque capacity."

Kevin Bender, Ergonomist
Ontario Ministry of Labour
2nd floor West Building phone: (416) 235-5322
1201 Wilson Ave fax: (416) 235-5080
Downsview, Ontario M3M 1J8
From: Enzerink

Take a look at the Human Factors Handbook. I do not have the data
immediately available, but I know it is in there. This data is mostly from
adult males in the US military, so values need to be lowered a bit for the
average population. The book also references torque values relative to
driver handle sizes, orientation, etc.
Good Luck. If you cannot find it, let me know and I'll look up the numbers
you need.

Robert Enzerink
Director, R&D
DePuy OrthoTech
From: Dhendry
The torque depends on the structure of the tool. The maximum torque is
infinite (as for Atlas)
From: Dhendry
The maximum practical torque is exerted with a T-shaped handle. This torque
is about 60 ft-lbs for a normal man (you can convert to Nm)
From: Margarita Vergara Monedero

A good reference is:
'Human force exertion in user-product interaction. Backgrounds for design'
B.J. Daams, 1994, Delf University Press, ISBN 90-6275-995-5
__________________________________________________ __________

Margarita Vergara Monedero Tfn. 34-964 34 56 80 Ext. 4757 Departamento
de Tecnologia
Fax 34-964 34 56 46 Universitat Jaume I
e-mail: vergara@tec.uji.es E-12071 Castello SPAIN
From: w.p.mossel@io.tudelft.nl (mossel, w.p.)

Dear Marco,
I found the following jounal articles in my files:

AU[ Pheasant, S., O'Neill, D.]
TI[ Performance in gripping and turning- A study in hand/handle
effectiveness] JN[ Applied Ergonomics]
YR[ 1975]
VO[ 6]
IS[ 4]
PG[ 205-208]

AU[ Nagashima, K., Konz, S.]
TI[ Jar lids: effect of diameter, gripping materials and knurling] PU[
Human Factors Society]
PL[ Dayton, Ohio]
YR[ 1986]
PG[ 672-674]

AU[ Bordett, Harvey M.; Koppa, Rodger J.; Congelton, Jerome J.] TI[ Torque
required from elderly females to operate faucet handles of various shapes]
JN[ Human factors]
YR[ 1988]
VO[ 30]
IS[ 3]
PG[ 339-346]

I think the first of the late Stephen Pheasant gives the best answer to
your problem.
He has also written two books:
Ergonomics, work and health, MacMillan, Basinstoke, 1991, ISBN
0-333-48998-5 Bodyspace,...Taylor & Francis, London, 1986, ISBN
Probably you can find something about your problem in it.
And there are values for the torque in:
Daams, B.J., Human Force exertion in user-product interaction, Delft
University Press, 1994, ISBN 90-6275-995-5

Hope this helps,

"All spelling errors due to line noise"
Kind regards, Vriendelijke groet, Grusze Wim Mossel

a.k.a. w.p.mossel@io.tudelft.nl
Phone: +31 15 278 35 64, Fax: +31 15 278 71 79 Address : Jaffalaan 9
2628 BX Delft
The Netherlands
From: "Paolo de Leva - Sport Biomechanics, Rome, IT"

non so se ti può servire, ma mi viene in mente che, come esperienza
insegna, il momento massimo è inferiore al massimo teoricamente
"possibile", perchè di solito la spinta esercitata dalla mano verso la vite
risulta insufficiente... e il cacciavite si sfila dalla testa della vite.
Questo non succede con una chiave a brugola (più consigliabile).


MARCO VICECONTI, PhD (viceconti@tecno.ior.it)
Laboratorio di Tecnologia dei Materiali tel. 39-51-6366865
Istituti Ortopedici Rizzoli fax. 39-51-6366863
via di barbiano 1/10, 40136 - Bologna, Italy

Tiger! Tiger! Burning bright in the forest of the night,
what immortal hand or eye could frame thy fearful symmetry?
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