Planking has roots in slavery. If you look at the picture above, it shows how slaves captured in Africa were stowed away on ships during the “Middle Passage” journey during the late 16th century. Slaves used the planks as beds. The act of “planking” became a fad by two guys traveling through England, but actual planking began at the start of the slave trade as captured African were transported by ships to the New World during the “Middle Passage.”
A plank collar is used on slave benches. It is a heavy wooden plank with five semicircular openings, when the plank is lifted it provides holding collars for five slaves. The plank is then chained down. The primary holding arrangement for women on the benches, however, is not chains. Each place on the bench is fitted with ankle and wrist stocks, and for each bench there is a plank collar, a plank which opens horizontally, each half of which contains five matching, semicircular openings, which, when it is set on pinions, closed, and chained in place, provides five sturdy, wooden enclosures for the throats of women. The plank is thick and thus the girls chins are held high. The plank is further reinforced between each girl with a narrowly curved iron band, the open ends of which are pierced; this is slid tight in its slots, in its metal retainers, about the boards, and secured in place with a four-inch metal pin, which may or may not be locked in place.
The diagram above is from a slave ship, according to Wikipedia.com, and depicts how captured Africans were stowed for shipment to markets in the New World. Unclothed, underfed, and forced to lie on hard planking in unhygienic conditions, many failed to survive the transatlantic voyage.