Both the Sharp MX-B42T and MX-B43T are black toner cartridges for the same printer family — the Sharp MX-B427 series (MX-B427W, MX-B427PW). They appear together in the compatible supplies list for that printer.

The key difference is page yield (capacity):

• MX-B42T — the standard cartridge with a yield of approximately 20,000 pages at 5% coverage, for the MX-B427, MX-B427W, and MX-B427PW.
• MX-B43T — this is the higher-yield version of the same cartridge for the same printer line. It offers a greater page yield, making it the better choice for higher-volume printing environments.

In Sharp's naming convention, this is a common pattern: the "T" suffix denotes a toner cartridge, and the numeric difference (42 vs. 43) typically indicates standard vs. high-yield variants for the same printer. The MX-B43T lets you print more pages per cartridge, reducing how often you need to replace it.

In short: Same printer compatibility, but the MX-B43T is the higher-capacity option. If you print heavily, the MX-B43T will save you money and hassle over time. If you're a lighter user, the MX-B42T is the more economical upfront purchase.