
General Information	Next: (continued)

SLINGS

WIRE ROPE

GENERAL INFORMATION

TABLE 1

CHOKER HITCH                                                 RATED

CAPACITY ADJUSTMENT

ANGLE OF CHOKER IN

RATED CAPACITY IWRC

DEGREES**

AND FC ROPE PERCENT

OVER 120

90 120

60 89

30 59

Figure 1.

0 29

NOMINAL SLING STRENGTH is based upon the nominal

**Percent of sling rated capacity in a choker hitch.

(catalog) rope strength of the wire rope used in the sling

CHOKER HITCH configurations affect the rated capacity

and other factors which affect the overall strength of the

of a sling.  This is because the sling leg or body is passed

sling.  These other factors include splicing efficiency, num

around the load, through one end attachment or eye.  The

ber of parts of rope in the sling, type of hitch (e.g. straight

contact of the sling body with the end attachment or eye

pull, choker hitch, basket hitch, etc.), diameter around

causes a loss of sling strength at this point.  If a load is

which the body of the sling is bent (D/d) and the diameter

hanging free, the normal choke angle is approximately 135

of pin used in the eye of the sling (Figure 1).

degrees.  When the angle is less than 135 degrees an

adjustment in the sling rated capacity must be made

(Figure 3).  As can be seen, the decrease in rated capacity

is dramatic.  Choker hitches at angels greater than 135

degrees are not recommended since they are unstable.

Extreme care should be taken to determine the angle of

choke as accurately as possible.

NOMINAL SPLICE EFFICIENCY is the efficiency of the

sling splice.  Any time wire rope is disturbed such as in

splicing an eye, the strength of the rope is reduced.  This

reduction must be taken into account when determining

the nominal sling strength and in calculating the rated the

Figure 2.

capacity.  Each type of splice has a different efficiency,

SLING ANGLE is the angle measured between a horizon

thus the difference in rated capacities for different types if

tal line and the sling leg of the body.  This angle is very

slings.  Nominal splice efficiencies have been established

important and can have a dramatic effect on the rated

after many hundreds of tests over years of testing.

capacity of the sling.  As illustrated above, when this prin

ciple applies whether one sling is used to pull at an angle,

in a basket hitch or for multi legged bridle slings.  Sling

angles of less than 30 degrees are not recommended.

Figure 4.

D/d ratio is the ratio of the diameter around which the sling

is bent divided by the body diameter of the sling (Figure

4).  This ratio has an effect on the rated capacity of the

Figure 3.

sling only when the sling is used in a basket hitch.  Tests

have shown that whenever wire rope is bent around a

diameter the strength of the rope is decreased.  Figure 5

illustrates the percentage of decrease to be expected.