A spad is a spike that looks similar to a small flat key, it has a round head with a hole and a long straight shaft with a round point. The spad is driven into a wooden plug in a hole in the roof of an underground mine by a spad gun, from this spad a plumbline is threaded.

The spads become survey station locations including the pointer spad station that allows the forman to align enteries from the main spad station. Each spads location is marked with it's station number using a brass tag, mining survey's are critical in tracking the mining process. Spad locations are considered sacred -- a missing spad in a critical location could create chaos, causing countless hours of additional work regaining control of the mine survey. In early mining days spad station surveying was often the means of determining a miners wages, by mapping advances in the coal seams.