This eBay item is a Nidec C33211-71A thermistor-controlled 12VDC 3-wire fan with tachometer signal.

This fan is Nidec's BetaV series, a ball-bearing fan. This fan was made in the USA.

The fan's speed is controlled by the fan's thermistor. The fan speeds up as the air it gets is too warm.

It is also possible to reduce the fan's speed by reducing the 12VDC supply.

The blue wire is the tachometer signal for monitoring the fan's RPM.

Nidec is one of three manufacturers that we found to be high quality, high reliability. (Sunon, NMB, Nidec)

I was unable to find a datasheet on this fan, but it is pretty common and standard.