Splicing – Wire Rope Slings

Hand Tucked Splice

A hand tucked splice is made by passing the wire rope around a thimble or forming an eye and splicing the dead end (short end) into the live end (long end) of the rope. Normally, each dead end strand is given one forming tuck and three full tucks around the same strand in the body of the rope. One additional full tuck is made when splicing more pliable wire ropes such as 6×37 classification.

A “forming tuck” is made by prying two adjacent strands apart, inserting a dead end strand into the opening and passing the strand under one, two, or three adjacent strands in the body of the rope. The dead end strand is set or locked tightly.

A “full tuck” is made by inserting a dead end strand under and rotating it one full 360 degree turn around a strand in the body of the wire rope. The tucked strand is set or locked tightly. Each subsequent full turn of the dead end strand around the live end strand constitutes an additional full tuck.

“Setting” or “locking” of a dead end strand is accomplished by pulling the strand end in under considerable force. A marlin spike is inserted in the same opening in the body of the rope ahead of the tucked strand and is rotated about the axis of the rope back to the start of the splice or toward the previous tuck. This helps set the tuck.

Certain end usages may indicate the desirability of special splices such as the Navy Admiralty Splice or logging splice. Splices made by these special methods may also attain the efficiencies used in calculating the rated capacity tables where the rope quality and number of tucks are equivalent to that outlined above. Development of such efficiencies should be confirmed by the sling fabricators making such splices.

Serving or wrapping of wire rope sling splices does not affect the splicing efficiencies nor rated capacities. Such servings are optional, although unserved splices are preferred because they permit visual inspection of the spliced area.

NOMINAL SPLICE EFFICIENCIES are measured in terms of efficiency (where efficiency = actual breaking strength of spliced termination divided by actual breaking strength of rope). This efficiency will change from splice to splice because of the many variable factors involved in producing the splice. Splice efficiencies given in Table 3 were established so that these normal variations are accommodated. The design factor used in establishing the rated capacities further assures that the sling will lift the load even in those rare instances when the splice efficiency falls slightly below the values given in the tables. Rated capacities shown in this manual have met with the most exacting test, that of the test of time and use in over fifty years of actual field experience.

Mechanical Splice

The returned loop is fabricated by forming a loop at the end of the rope, sliding one or more metal sleeves over the short end of the loop eye and pressing these sleeves to secure the end of the rope to the sling body. This makes an economical sling and in most cases one that will give satisfactory service. A drawback to this type of sling is that the lifting capacity of the sling depends 100% upon the integrity of the pressed or swaged joint. Should the metal sleeve(s) fail, the entire eye will also fail.

Notice that the splice efficiency factor plays no role in the calculation of the Choker Hitch rated capacity. This is because as the rope passes through the eye of the sling in a choke, the weakest part of the sling is in the body of the sling at the choke point. Thus the splice being higher in efficiency, has no effect on the rated capacity, because the efficiency factors are not additive. 

Rated capacities for single part, choker and basket hitches are calculated exactly the same as for hand tucked slings except for the nominal splice efficiencies. The rated capacities adjustment table 1 for choker hitches also applies for mechanical splice slings. Minimum D/d ratio for basket hitches is 25. This larger D/d ratio is required because the Nominal Splice Efficiency is higher.