Odd size on anchor chain?

S

SFS

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Aug 18, 2015
2,070
Currently Boatless Okinawa
OK, here is today's puzzle. I measured my anchor chain today with my calipers, in preparation for ordering a Mantus swivel. Caliper read 0.338 inches. Not a decimal equivalent of a fraction I could think of immediately, so I measured another link, and got 0.337 inches. Measured a third link, and got 0.338. I love the precision, but I'm stumped.

3/8" would be 0.375", 5/16" would be 0.3125", 11/32" would be 0.3437". What gives? Am I measuring incorrectly? I put the calipers on the diameter of long straight side section of a link. The chain is not rusted, and the galvanizing is in good shape and seems very uniformly distributed.

Or did the PO buy 8.6 mm chain?
 
S

SFS

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Aug 18, 2015
2,070
Currently Boatless Okinawa
Just found an online website that lists their 5/16" as nominally 0.330" diameter. Maybe this is 5/16" (regardless of the math).
 
Charles Erwin

Charles Erwin

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Jan 30, 2012
1,123
Nor'Sea 27 "Kiwanda" Portland/ Anacortes
Look at a link and see whether it is marked A4, G4, B3, something else, or maybe not marked at all. Then find the table that matches the embossed mark. My notes say G4 or A4 is .330" but designated 5/16 11.7 links per foot. 3B is .343 and likewise designated 5/16" 12 links per foot.

Pretty sure the embossing is on 5/16 and up 3B and every size of G4. ACCO has the tables in its catalog at http://www.newmorning.info/page65/files/Acco Chain Catalog.pdf

For what it is worth - measured a lot of chain - I never had one case that was a dead match to the table.

Charles
 
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S

SFS

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Aug 18, 2015
2,070
Currently Boatless Okinawa
Charles, you are my new hero for that last comment. And next time on the boat, I will see how many links per foot it is, and look for the embossing mark.
 
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S

SFS

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Aug 18, 2015
2,070
Currently Boatless Okinawa
@BudGates - I considered that in the OP as well. How common is metric sized chain in the US, and is 8.5 a common size of metric chain?
 
S

SFS

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Aug 18, 2015
2,070
Currently Boatless Okinawa
Interesting chart, and obviously incorrect in many places. For the table that covers the short-link version of this chain, the measurement for "inside length" is the same as the measurement for "outside length", for many of the listed sizes (including the 8.5 mm). Doesn't inspire confidence in the company's ability to hand out correct specifications.
 
BudGates

BudGates

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Apr 19, 2012
1,043
O'Day Daysailor 17 Nevis MN
SFS said:
Interesting chart, and obviously incorrect in many places. For the table that covers the short-link version of this chain, the measurement for "inside length" is the same as the measurement for "outside length", for many of the listed sizes (including the 8.5 mm). Doesn't inspire confidence in the company's ability to hand out correct specifications.
Click to expand
According to both the drawing and the second chart "b" is the outside width not outside length as it says in the first chart. It stands to reason that they would be close if not the same.
 
S

SFS

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Aug 18, 2015
2,070
Currently Boatless Okinawa
Ah, now I can translate the odd symbols to "b" and "d". Yeah, it makes sense that the two would be close on a short link chain. Column header sure is misleading.
 
M

MitchM

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Jan 20, 2005
1,020
Nauticat 321 pilothouse 32 Erie PA
and remember if you have a windlass that you need HT or BBB anchor chain, in the compatible size for your windlass gypsy.
 
Ron20324

Ron20324

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Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
[QUOTE="MitchM, if you have a windlass that you need HT or BBB anchor chain, in the compatible size for your windlass gypsy. [/QUOTE]

And you can get gypsies in differing sizes for most windlasses.
 
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