This 256MB 144-pin DDR2 memory DIMM Upgrade is designed for use with HP color LaserJet Pro 300 series. It will run at higher speed (533MHz/PC2-4200) than the standard HP CB423A (which is PC2-3200 at 400MHz). However, this product is not recommended for printer models other than the Pro 300 and 400 series. it is guarranteed 100% compatibility with your Pro 300 M375nw, M351a, M351 and M357nw printers.