This is the 4-ohm version of the Pioneer W25GR31-51F (8 ohms).
It has a rubber surround and pulp cone. The power rating is 90 Watts RMS.
The T/S parameters are:
fs = 26 Hz
Qts = .34
Vas = 4.77 cu ft
Cutout diameter is 9-1/8", mounting screw circle diameter is 9-5/8".
This driver would make an excellent subwoofer for home or car. It provides a bass response of 36 Hz in a 2.4 cu ft ported box tuned to 31 Hz. Contact me if you want box design help, I'm the author of the Car Stereo Cookbook and designer of the Subwoofer Design Toolbox software.