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The Tinkertoy Construction Set is a toy construction set for children. It was created in 1914—one year after the A. C. Gilbert Company's Erector Set—by Charles H. Pajeau and Robert Pettit in Evanston, Illinois. Pajeau, a stonemason, designed the toy after seeing children play with sticks and empty spools of thread. He and Pettit set out to market a toy that would allow and inspire children to use their imaginations. At first, this did not go well, but after a year or two over a million were sold.
The cornerstone of the set is a wooden spool roughly two inches (5 cm) in diameter with holes drilled every 45 degrees around the perimeter and one through the center. Unlike the center, the perimeter holes do not go all the way through. With the differing-length sticks, the set was intended to be based on the Pythagorean progressive right triangle.
Tinkertoy sticks before 1992 were made with a diameter of 0.25 inch. The earlier sets had natural wood sticks, but changed to colored sticks in the late 1950s. From measurement, the orange sticks are 1.25 inches long; yellow, 2.15; blue, 3.35; red, 5.05; green, 7.40; and, purple, 10.85. Spools are 1.35 inches in diameter with holes of 0.30 inch depth. The ratio of succeeding stick sizes when including adjustments for spool diameter and hole depth work out to be the square root of 2, enabling the construction of 45-45-90 right triangles (see Pythagorean theorem). The theory is discussed in Pajeau's patent, no. 1113371, of 1914.
The sets were introduced to the public through displays in and around Chicago which included model Ferris wheels. Tinkertoys have been used to create surprisingly complex machines, including Danny Hillis's tic-tac-toe-playing computer (now in the collection of the Computer History Museum in Mountain View, California) and a robot at Cornell University in 1998.
Hasbro owns the Tinkertoy brand and currently produces both Tinkertoy Plastic and Tinkertoy Classic (wood) sets and parts.
Standard parts 
In addition to the previously described spools, a standard Tinkertoy set includes:
- Wheels, which are thinner than spools, but larger in diameter. Like spools, their center holes have a snug fit.
- Caps, originally wooden, but later plastic, cylindrical pieces with a single blind axial hole snugly fitted to the rods.
- Couplings, small cylindrical pieces (originally wood; later plastic) approximately 2 inches long and half an inch in diameter, with snug-fitting blind-drilled holes in either end, and a loose-fitting through-drilled hole crosswise through the center of the part.
- Pulleys, identical to spools, except that the center holes are loose-fitting.
- "Part W", approximately the same size and shape as a spool, but with perimeter holes 90 degrees apart, loose-fitting center holes, and four tight-fitting through-drilled holes parallel to the center hole. This allowed for free-spinning parts, and also for construction of "cage" or "lantern" gears.
- Short pointed sticks (originally wood, but later plastic), typically red, and flags ("fan blades,") typically green plastic, and various other small parts.
Spools and pulleys all have a single groove around the outside; "Part W" has two parallel grooves.
Sticks (or "rods") are slotted on each end, both to provide some "give" when inserted into snug-fitting holes, and to allow thin cards, flags, and strings to be inserted into the slots. They are color-coded by size; in the 1960s-era sets, they were, in order from shortest to longest, orange, yellow, blue, red, green, and violet. Each successively longer rod is (with allowances for the size of the spools) next smaller size times the square root of two; thus any two of the same size will combine with one of the next size up, and three spools, to form an isosceles right triangle.
Most of the larger sets also include a driveshaft (an unfinished wooden rod without slotted ends, of an intermediate length between "green" and "violet," normally turned with a small plastic crank.
Sets with battery-powered electric motors were available; these sets also typically included at least one wooden "double pulley," with a single snug-fitting through-drilled center hole, and grooved rims at two diameters, allowing different moving parts to operate at different speeds.
- Strange, Craig. Collector's Guide to Tinker Toys. ISBN 0-89145-703-8.
- Dewdney, A. K. The Tinkertoy Computer and Other Machinations. ISBN 0-7167-2491-X.