I have noticed around the web that there seems to be some confusion among us about what a rated shackle is really rated for. I just thought that I'd post some info on the subject for reference.
A rated shackle will have the working load limit (WLL)stamped or raised on the body of the shackle. There are basically two types, carbon steel and alloy steel. Known as grade A (carbon steel) or B (Alloy steel).
The chart from Fed spec RR-C-271D sets the load standards for rated shackles. It is the amendment to RR-C-271D that is the current standard. It is available at http://www.lexcocable.com/shackles-screw-pin-anchor-shackles.html at the middle of the page. You want table XVII on page 4 of the PDF
Here is the relavent text from RR-C-271D laying out the standards. I boldfaced some I thought especially important.
3.5.3 Type IV, shackles.
3.5.3.1 General. Grade A shackles, together with their pins and bolts shall be forged from carbon steel. Grade B shackles together with their pins and bolts shall be forged from alloy steel as specified in 3.1.1.2.4.
3.5.3.1.1 Threads. Screw-pin shackles shall be threaded after fabrication to final size and shape. Threads shall conform to FED-STD-H28 for Unified Coarse (UNC) thread unless the corresponding fine threads are specified (see 6.2). Threads on zinc-coated or self-colored finished shackles shall be not looser than class I fit. The male threads of zinc-coated shackles may be undercut, as necessary, so that after coating they will properly mate (not less than class 1 fit) with the standard size female threads.
3.5.3.1.2 Proof loads. Shackles shall withstand the proof loads shown in table XVII (see 4.4.2.2.1) without developing surface rupture or defects that would interfere with serviceability or prevent disassembly of the pin. After proof loading, screw-pin shackles shall be disassembled by hand after the first turn.
3.5.3.1.3 Breaking loads. Without breaking, shackles shall withstand the breaking loads shown in table XVII (see 4.4.2.2.2).
3.5.3.1.4 Safe working load. The recommended safe working loads of shackles covered by this specification are shown in table XVII for information purposes.
3.5.3.1.5 Ductility. Shackles shall be sufficiently ductile so that, when fractured, the fractured member shall show a permanent distortion before breaking. If the pin fractures, it shall show a permanent bend of not less than 20 degrees. If the body fractures, it shall show a permanent mid-shackle set of not less than 15 percent of the original spread between bows.
3.5.3.1.6 Marking. Each shackle body shall be permanently and legibly marked in raised or stamped letters on the side of the shackle bow with the identifying manufacturer's name or trademark, shackle size, and the recommended safe working load. Grade A regular strength shackle pins and bolts shall be unmarked; grade B high strength shackle pins and bolts shall be marked by the raised or stamped letters "HS" on the head. Shackle markings shall be raised or stamped letters or figures of the maximum practical height permitted by the size of the shackle component being marked, but not to exceed 3/4 inch in height by 1/8 inch in relief. Stamping dies shall be of the round bottom, low stress type. Marking location shall not interfere with the serviceability of the shackle assembly.
3.5.3.1.7 Finish. Unless otherwise specified (see 6.2), shackle components shall be zinc coated as specified in 3.3.1.4.
3.5.3.2 Form and dimensions. The form of the respective shackle types and classes shall be similar to that shown on figures 19 and 20 (see 6.2). Dimensions of shackle bodies and component pins and bolts shall conform to the dimensional requirements specified in table XI through XVI.
So, as you can see, It may be that we should consider the proof load as maximum on these shackles under normal winching use.. As the proof load is a minimum rated load where the shackle will not deform. Of course, in an emergency, It can be taken all the way to breaking!
I find it interesting and humorous that the rating system says the shackle must withstand the breaking load without breaking! Not that the idea is without merit. It sets a limit that to exceed is at great peril. Beyond the breaking limit, 'There be Dragons'....
A rated shackle will have the working load limit (WLL)stamped or raised on the body of the shackle. There are basically two types, carbon steel and alloy steel. Known as grade A (carbon steel) or B (Alloy steel).
The chart from Fed spec RR-C-271D sets the load standards for rated shackles. It is the amendment to RR-C-271D that is the current standard. It is available at http://www.lexcocable.com/shackles-screw-pin-anchor-shackles.html at the middle of the page. You want table XVII on page 4 of the PDF
Here is the relavent text from RR-C-271D laying out the standards. I boldfaced some I thought especially important.
3.5.3 Type IV, shackles.
3.5.3.1 General. Grade A shackles, together with their pins and bolts shall be forged from carbon steel. Grade B shackles together with their pins and bolts shall be forged from alloy steel as specified in 3.1.1.2.4.
3.5.3.1.1 Threads. Screw-pin shackles shall be threaded after fabrication to final size and shape. Threads shall conform to FED-STD-H28 for Unified Coarse (UNC) thread unless the corresponding fine threads are specified (see 6.2). Threads on zinc-coated or self-colored finished shackles shall be not looser than class I fit. The male threads of zinc-coated shackles may be undercut, as necessary, so that after coating they will properly mate (not less than class 1 fit) with the standard size female threads.
3.5.3.1.2 Proof loads. Shackles shall withstand the proof loads shown in table XVII (see 4.4.2.2.1) without developing surface rupture or defects that would interfere with serviceability or prevent disassembly of the pin. After proof loading, screw-pin shackles shall be disassembled by hand after the first turn.
3.5.3.1.3 Breaking loads. Without breaking, shackles shall withstand the breaking loads shown in table XVII (see 4.4.2.2.2).
3.5.3.1.4 Safe working load. The recommended safe working loads of shackles covered by this specification are shown in table XVII for information purposes.
3.5.3.1.5 Ductility. Shackles shall be sufficiently ductile so that, when fractured, the fractured member shall show a permanent distortion before breaking. If the pin fractures, it shall show a permanent bend of not less than 20 degrees. If the body fractures, it shall show a permanent mid-shackle set of not less than 15 percent of the original spread between bows.
3.5.3.1.6 Marking. Each shackle body shall be permanently and legibly marked in raised or stamped letters on the side of the shackle bow with the identifying manufacturer's name or trademark, shackle size, and the recommended safe working load. Grade A regular strength shackle pins and bolts shall be unmarked; grade B high strength shackle pins and bolts shall be marked by the raised or stamped letters "HS" on the head. Shackle markings shall be raised or stamped letters or figures of the maximum practical height permitted by the size of the shackle component being marked, but not to exceed 3/4 inch in height by 1/8 inch in relief. Stamping dies shall be of the round bottom, low stress type. Marking location shall not interfere with the serviceability of the shackle assembly.
3.5.3.1.7 Finish. Unless otherwise specified (see 6.2), shackle components shall be zinc coated as specified in 3.3.1.4.
3.5.3.2 Form and dimensions. The form of the respective shackle types and classes shall be similar to that shown on figures 19 and 20 (see 6.2). Dimensions of shackle bodies and component pins and bolts shall conform to the dimensional requirements specified in table XI through XVI.
So, as you can see, It may be that we should consider the proof load as maximum on these shackles under normal winching use.. As the proof load is a minimum rated load where the shackle will not deform. Of course, in an emergency, It can be taken all the way to breaking!
I find it interesting and humorous that the rating system says the shackle must withstand the breaking load without breaking! Not that the idea is without merit. It sets a limit that to exceed is at great peril. Beyond the breaking limit, 'There be Dragons'....
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