Mid-way through the production run for the 2001 model year Ford changed the design of the water pump on the 4.6L engine. The older style pump produced from 1996 to mid-2001 had a longer shaft. In January of 2001 the design of the pump was changed to a shorter shaft. This necessitated a change in the design of the pump pulley.
Refer to the pictures below to see which pulley design you have so you can order the correct one for your application.
1992-2001.5 4.6L 2 valve SOHC:
2001.5-2011 4.6L 2 valve SOHC:
