For a Mercury 115hp outboard, the stock prop is usually a 21-pitch aluminum prop , but the exact size can vary by year, gearcase, and whether it’s a standard or Command Thrust model. Mercury’s prop selector is the safest way to confirm the factory setup for your exact engine.

What’s typical

  • Many Mercury 115 setups come from the factory with a 21P aluminum prop.
  • Some 115 Command Thrust applications use a larger-diameter, lower-pitch prop instead, often in the 12–16 pitch range depending on hull and setup.
  • Aftermarket fitment guides also show that Mercury 115 applications can vary by gearcase and shaft type, which changes the prop match.

Best way to verify

  • Check the engine serial number.
  • Look at the current prop stamping on the hub.
  • Use Mercury’s prop selector for the exact model and boat setup.

Practical note

If you’re swapping from stock, a 19P stainless prop is often discussed as a performance upgrade on some 115 setups, but that depends heavily on boat weight, load, and target RPM.

TL;DR

Most standard Mercury 115hp outboards are commonly found with a 21-pitch aluminum stock prop , but Command Thrust and other variants can differ.