With Monroes M33X printing calculator ribbon cartridge youll never have to worry about a messy installation process ever again! The NEW Monroe M33X Black/Red Ribbon Cartridge is the first-ever Monroe ribbon cartridge that can be used across an entire line of Monroe printing calculator models. This ribbon cartridge is compatible with all Monroe X Series printing calculators, featuring the highest standards in the calculator industry. Monroes ribbon cartridges produce the darkest printing black/red ribbon cartridges on the market using our exclusive True Red color. True Red ink is the perfect red specifically made by Monroe, and doesnt have the orange tint you see in watered down versions from other brands. Our ribbon cartridges have the highest possible inking degree, and are virtually smudge-free! To maintain the darkest print, we recommend users change their Monroe M33X ribbon cartridges after replacing 2 paper tape rolls.