A threshing-board is an obsolete farm implement used to separate cereals from their straw; that is, to thresh. It is a thick board, made with a variety of slats, with a shape between rectangular and trapezoidal, with the frontal part somewhat narrower and curved upward (like a sled or sledge) and whose bottom is covered with lithic flakes or razor-like metal blades.

One form, once common in the Mediterranean Sea area, was "about three to four feet wide and six feet deep (these dimensions often vary, however), consisting of two or three wooden planks assembled to one another, of more than four inches wide, in which several hard and cutting flints crammed into the bottom part pull along over the grains. In the rear part there is a large ring nailed, that is used to tie the rope that pulls it and to which two horses are usually harnessed; and a person, sitting on the threshing-board, drives it in circles over the cereal that is spread on the threshing floor. Should the person need more weight, he need only put some big stones over it." «…de tres a cuatro pies de ancho y unos seis de largo, variando frecuentemente estas dimensiones, y se compone de dos o tres tablones ensamblados unos con otros, de más de cuatro pulgadas de grueso, en los que se hallan embutidas por su parte inferior muchos pedernales muy duros y cortantes que arrastran sobre las mieses. En la parte anterior hay clavada una argolla para atar la cuerda que le arrastra, y a la que se enganchan comúnmente dos caballerías; y sentado un hombre en el trillo lo conduce dando vueltas sobre la parva extendida en la era. Si el hombre necesita más peso, pone encima piedras grandes».

The dimensions of threshing boards varied. In Spain, they could be up to approximately two meters in length and a meter and a half wide. There were also smaller threshing-boards, as little about a meter-and-a-half long and a meter wide.The big threshing-boards were intended for a "yoke" or pair of draft animals (oxen or mules), whereas the smaller ones were indended to be drawn by a single animal The thickness of the slats of the threshing-board is some five or six centimeters. Nonetheless, since threshing-boards are nowadays custom made, made to order or made smaller as an adornment or souvenir, they may range from miniatures up to the sizes previously described.There are specialized original threshing-boards for garbanzos, with smaller dimensions than those used for cereal grains; also, at times, instead of stone chips, they have rollers with crammed blades: "threshing carts" («trillo de ruedas») known in antiquity as Plostellum punicum.

The threshing-board has been traditionally pulled by mules or by oxen over the grains spread on the threshing floor. As it was moved in circles over the harvest that was spread, the stone chips or blades cut the straw and the ear of wheat (which remained between the threshing-board and the pebbles on the ground), thus separating the seed without actually damaging it. The threshed grain was then gathered and set to be cleaned by some means of winnowing.

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