Koyo radiator cap?

[Dark Lord]

Today I just installed a Koyo radiator. The cap from my stock radiator doesn't fit, neither does an aftermarket one I picked up at Autozone. The auction I bought the Koyo from on eBay didn't mention anything about my radiator cap not being compatible. Can anybody shed some light on this?

 

[LittleCaesar]

Which Koyo radiator did you buy? It needed to be 1998A. My stock one fit just fine.