Acer 4GB DDR3 1333MHz, 4 GB, 1 x 4 GB, DDR3, 1333 MHz, 240-pin DIMM

Why do I find that the same product is available on different item numbers?

Manufacturers often release the same product with different item numbers, typically just different versions of the packaging. For example, the packaging may be targeted at different countries. We try our best to unify the products, but it can happen that the same product appears on different item numbers in our system.