ESR Underdrive pulley/all underdrive pulley question

[Get Slideways S13]

I am new to this forum, but i know that searches must be done before posting, and i did that and found nothing so i am asking this question. I just purchased an underdrive pulley of ebay and need to know what size belts i need to buy for it. The underdrive pulley i purchased was from ESR Racing. Anyone else bought the same one or anyone else bought an underdrive pulley and can tell me what belts I need to buy. thank you.

[Structure240sx]

try to contact the company

if that doesnt work next best idea would be to contact asp or unorthodox and get the part numbers from them. sorry i dont have mine anymore