Description
Parallels come in pairs of two, which are machined to be the same dimensions their corresponding faces. They come in a variety of thicknesses and size, allowing them to be stacked up or to support a workpiece which doesn't have a flat profile. Parallels commonly have a series of holes drilled on the 'front' face - allowing them to be used to position a workpiece or secured using t-slot clamps, and a countersink on each side to remove any sharp edges.
Generally, workshop parallels have 4 faces that are machined and ground - the front, back and sides, although some do have the ends with a smooth surface. The surface of a parallel can often tell how it was manufactured, with a 'grain' showing that it was ground - and a smooth or mirrored finish showing it has been lapped. Parallels that have a good surface tolerance can be lightly bonded together by sliding or rotating two parallels together, and the smooth surfaces allows a temporary molecular-attraction to take place - this is known as Wringing and is also found with gauge blocks.
Read more about this topic: Parallels (engineering)
Famous quotes containing the word description:
“To give an accurate description of what has never occurred is not merely the proper occupation of the historian, but the inalienable privilege of any man of parts and culture.”
—Oscar Wilde (1854–1900)
“It [Egypt] has more wonders in it than any other country in the world and provides more works that defy description than any other place.”
—Herodotus (c. 484–424 B.C.)
“I fancy it must be the quantity of animal food eaten by the English which renders their character insusceptible of civilisation. I suspect it is in their kitchens and not in their churches that their reformation must be worked, and that Missionaries of that description from [France] would avail more than those who should endeavor to tame them by precepts of religion or philosophy.”
—Thomas Jefferson (1743–1826)