• Rigging Hardware – Turnbuckles

    Information about specification and application for turnbuckles is given in this article.

    Specification

    Turnbuckles are made as per Federal Specification FF-T-791b, ASME B30.26 and ASTM F-1145.

    Federal Specification FF-T-791b covers swaged, welded, cast or forged turnbuckles with and without jam nuts. Three types and four form of turnbuckles are made as per this specification as under.

    Type I – Open turnbuckle bodies
    Form:
    1 – Forged
    2 – Spread
    3 – Resistance welded and
    4 – Arc or gas welded.
    Type II – Pipe turnbuckle bodies and
    Type III -Rigging turnbuckle bodies.

    They are made in eight classes as under.

    1 – Turnbuckle, body only without end pulls, heads not drilled.
    2 – Turnbuckle, body only without end pulls, heads threaded right and left hand.
    3 – Turnbuckle with stub and stub end pulls, complete.
    4 – Turnbuckle with eye and eye end pulls, complete.
    5 – Turnbuckle with hook and hook end pulls, complete.
    6 – Turnbuckle with hook and eye end pulls, complete.
    7 – Turnbuckle with jaw and jaw end pulls, complete.
    8 – Turnbuckle with jaw and eye end pulls, complete.

    Class 4 to Class 8 turnbuckles of Type I, Form 1 (Forged) are shown below.

    Turnbuckles

    Turnbuckles and end pulls are made from steel of a grade which will meet recommended working load limits specified by the specification.

    They are made with design factor of 5:1 and recommended working load limits in Pounds for nominal outside diameter of threads in inch are as under.

     

    Size (inch) Type I, Form 1 All Others
    Jaw, eye or stub end pulls Hook end pulls Jaw, eye or stub end pulls Hook end pulls
    ¼ 500 300 310 210
    5/16 700 500 540 330
    3/8 1040 700 820 460
    ½ 1800 1040 1500 740
    5/8 2700 1600 2400 1080
    ¾ 4000 2000 3600 1500
    7/8 5800 2400 5000 2000
    1 7600 2900 6600 2560
    1 ¼ 12000 4600 10700 4120
    1 3/8 14400 5800 12600 4860
    1 ½ 17000 7200 15500 5860
    1 ¾ 23000 - 21000 -
    2 30000 - 27600 -
    2 ¼ 39400 - 36200 -
    2 ½ 48400 - 44600 -
    2 ¾ 60800 - 55400 -
    3 70000 - 67400 -
    3 ¼ 80000 - 80000 -
    3 ½ 95000 - 95000 -
    3 ¾ 110000 - 110000 -
    4 127000 - 127000 -

     

    Note:
    As steel is selected by manufacturer, turnbuckles offered by some manufacturers have higher safe working load than specified by above specification.

    Turnbuckles bodies and ends are available in standard lengths. For dimensional detail, please refer the specification or Crosby’s General Catalog.

    Application

    Turnbuckles are recommended for straight or in-line pull only.

    Generally open forged turnbuckles are used for hoisting and rigging operations.

    If a turnbuckle is used in an application where vibration is present, the end fittings should be secured to the frame with lock pins or wires to prevent them from turning and loosening.

    Lock nuts are available for all sizes of turnbuckles.

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