The Polyurethane/Kevlar is the standard belt supplied with the skimmers. Low cost and durable. This belt performs well in 99 percent of applications.
Replacement Parts for Skimpy Standard model
How to select the correct belt for your El Niño skimmer
The skimmer sizes are based on how far they reach down from the bottom of the motor. The belt size will be the same as the reach of your skimmer.
Method 1
Lay the belt flat on a table and measure the length. Take that measurement and subtract 3 inches. This will give you the correct belt size.
Method 2
Measure the distance from the centerline of the top pulley to the centerline of the bottom pulley. Subtract 1.75" from that measurement and that will give you the correct belt size for your skimmer.

Standard Model 3 & 3.1
lower pulley axle
$1.50 each

Standard Model 3
replacement motor for Ser# on the
cover has AN or NA at the end
$29.99 each