cow
A chock: a wedge or brake used to stop a machine or car.
cow: a wedge that stops a loaded mine car
A cow is a heavy wooden or metal wedge driven beneath the wheel of a loaded mine car to lock it in place on the rails. In underground mining operations, especially in coal mines, loaded cars sit at steep grades or on level track waiting to be hauled to the surface. A single cow, often a tapered block of hardwood or cast iron, prevents the car rolling forward under its own weight or the weight of the load, which can exceed 5 tons. The wedge is hammered in tight against the wheel flange.
The term appears in mining records from the 19th century onward, though its origin is unclear. It may derive from the idea of immobilizing something as completely as one might pen livestock, or it may simply be colloquial shorthand for a blunt, heavy object. In some coal regions, the device was also called a scotch or chock, though these terms sometimes refer to slightly different braking methods.
Cows are crude but effective. A mine worker would carry one or more wedges in his pocket or belt, driving the cow under the downhill wheel of any car that needed to stay put. Because mine cars run on narrow-gauge track, often with worn or irregular wheels, the fit between wheel and wedge varies. A poorly seated cow could slip under vibration or load shift, allowing the car to move. Corrosion and impact damage to the wedge itself reduced its grip over time.
The real danger lay in complacency. A car held by a single cow on a slope could kill a worker if it broke free and rolled. Best practice required multiple wedges, one under each wheel, and chains or props as backup on steeper inclines. In mechanized operations after the 1930s, as gravity-fed hoists and powered brakes became standard, the hand-wedged cow fell out of use in main mine roads, though it persisted in tramway work and on sidings.
Today, the cow survives mainly in heritage operations and in the language of older miners. Modern mines use mechanical and hydraulic brakes, load limiters, and rail ramps. Yet the principle endures: stop a rolling car with a passive wedge, and do it right the first time.