You can see this part as Ref # 112 highlighted on the bottom of the diagram shown here.

Product Details:

• Pulley Base.
• Made by Hypro.
• Part # 9910-800311.
• Replacement Part For The Following Pump Model #s: 9910-D252GRGI, 99100-D252GRGI58, And 9910-D252.
• Requires 1 Part Per Pump.