The knitting yarn called 'Seaman's Irons' is size 2/6 worsted count.

That is two strands of size 6 thread twisted together.

The size 6 thread means that 6 standard length skeins (560 yard) of it can be made from one pound of fleece.

It is a strong yarn used to make the fisher ganseys, and ganseys for other workmen, traditionally knitted in the round.

Probably just a coincidence.