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Both bands will be one Fathom wide and composed of 36 ribbons. So, each ribbon will occupy half a 'Handbreadth' or two inches.
Image: Vitruvian Man by Da Vinci (source)
A Fathom is a unit of length used to measure the depth of water or the length of a nautical rope or cable, equal to 6 ft (1.8288 m)
Verb
1. to measure the depth of; sound
2. to get to the bottom of; understand thoroughly
Etymology
ME fadme fæthm (akin to OFris fethm, OS pl. fathmōs), the two arms outstretched (to embrace, measure), akin to German faden, thread
From: www.yourdictionary.com