IMPORTANT FACTS
ABOUT CRIMPING
CRIMPING: THEN AND NOW
The first multi-pin connectors were
terminated by soldering the conductor
to non-removable contacts. However,
high temperature applications and
the need for simple and reliable field
service led to the introduction of
connectors with removable contacts.
These were crimped onto the con-
ductor rather than being soldered.
The first standard crimp tool
developed to crimp these new con-
tacts was introduced in the early
sixties. MS3191-1, a military drawing,
defined this tool and its accessories.
The MS3191-1 utilized a four indent
crimp pattern together with a positive
stop locator which controlled the travel
of the indenters (crimp depth).
The MS3191-1 design was a
compromise between simplicity of
operation and crimp performance
since the crimp depth for any given
contact was not adjustable to accom-
modate the differing diameters of the
conductors to which it would be
crimped. It was, however, suitable for
the crimp connectors of that era.
An improved tool design featuring
independently adjustable crimp depths
was soon introduced as MS3191-4.
The MS3191-4 had an internal adjust-
ment, totally independent of the loca-
tor, which permitted the selection of
seven separate crimp depths, allowing
optimal crimping of conductors rang-
ing from AWG 12 to 26 regardless of
the wire barrel size of the contact.
MS3191-4 also introduced the
use of the double tipped indenter to
produce an eight indent crimp pattern
which has consistently achieved
superior tensile pull off values.
MS3191-4 introduced the concept
of a turret head containing three loca-
tors which could be used without
separating any of them from the basic
crimp tool.
In 1969 two military specifications
for crimp tools were developed to
replace the existing military drawings.
They were MIL-T-22520C (Navy) and
MIL-T-83724 (USAF) which defined a
standard size crimp tool similar to the
MS3191-4, but with an expanded
eight step crimp depth range. These
specifications also defined a miniature
crimp tool to crimp conductors as
small as AWG 32.
Both documents were combined
in 1971 into MIL-C-22520D. All
previous military standards for crimp
tools were then cancelled including
the MS3191.
MIL-C-22520 has since replaced
many other crimp tool documents
including: MS3198, MS22910,
MS17776, MS28731, MS90388,
MS14037, MS27437, MS27828,
MS27832, MS55619, MS27426 and
others. This list includes specifications
for indent crimp tools, terminal lug
crimp tools, pneumatic tools, coaxial
cable crimp tools and connectors
service kits.
The establishment of MIL-C22520
was a milestone on the road to crimp
tool standardization. Its development
has eliminated the waste and confu-
sion which accompanied the overlap-
ping applications of many different
“standard” crimp tools called out by a
deluge of unrelated military drawings.
MIL-C-22520D for the first time
established a single specification which
set forth performance requirements for
all crimp tools to be used on military
standard electrical connectors.
THE CRIMPING CONCEPT
Crimping is a method of firmly
attaching a terminal or contact end to
an electrical conductor by pressure
forming or reshaping a metal barrel
together with the conductor. The
forming of a satisfactory crimp
depends on the correct combination
of conductor, crimp barrel and tool.
When applied with a properly
matched tool a union would be
established which has both good
electrical and mechanical characteris-
tics. The tool will provide these
requirements consistently and reliably
with repeatability assured by quality
cycle controlled tooling. There are
several common configurations of
crimped joint; several examples are
shown below.
The electrical resistance of a
properly designed and controlled
crimped joint should be equal to, or
less than, the resistance of an equal
section of wire. Specifications state
the requirements in terms of millivolt
drop at a designated current.
The mechanical strength of a
crimped joint and hence its pull-out
force (tensile strength), varies with the
deformation applied. Therefore, by
properly shaping the deformation a
high pull-out force can be achieved,
i.e. the crimp die of the tool deter-
mines the crimp configuration and
deformation.
The dies in the tool determine the
completed crimp configuration which
is generally an element of contact
and/or connector design. Some of the
design considerations are: a) The type
of contact, its size, shape material and
function, b) The type and size of wires
to be accommodated, c) The type of
tooling into which the configuration
must be built.
EIGHT INDENT
FOUR INDENT
TWO INDENT
HEXAGONAL CRIMP
CIRCULAR CRIMP
B CRIMP
NEST & INDENT CRIMP
CAPTIVE CRIMP
INSULATION DISPLACEMENT
DANIELS
MANUFACTURING
CORPORATION
®
© COPYRIGHT 2003 DANIELS MANUFACTURING CORPORATION PAGE 3
Tooling Guide CD pages 2/11/03 2:56 PM Page 3