In early times, bronze spades had most likely been used as exchange mediums. The spade coins were imitations of the real spades that were easier to carry. There has been discovered several tools of this type.

Wang describes two types (p. 90-92), and compares them to the spade coins: the tools had a hollow handle with a hole, where the shaft was secured with a strap. To make the spade stronger, the socket projected onto the blade and it had protruded reinforcement lines on the blades.

The early types looked more like the real tool, than the later ones. In time the spade coins became lighter, thinner and increasingly stylized. The handle was no longer hollow and the slight concave shape of the sharp end of the blade became deeper, so the spade coins got the resemblance of a human.

The other name Qian has also been used for the spade money in the historical literature. Wang says that Qian was another type of spade, and that each of them was imitated for a type of coin (p. 97-98). Since the coins did no longer look like the tools, there has been a need to have specific names for tools and for coins, so the name for the tool spades became Bo and Tao and the names for the spade coins became Bu and Qian.

Later the Bu became the designation for spade coins. When the round coins came into use, Qian became the name for money in general, which it actually still is today. The monetary unit for the Bu spades were the jin , which also meant axe. Axes had also been exchange objects like spades and knives. Another unit used for the spade coins were the liang . The earliest evidence of true coinage were, according to Wang (p. 106), an ode in the early text Shiji. This text was from the Western Zhou and written no later than the 7th. century B.C. This means we can date the spade coins at least this far back, but it was probably much earlier.