The propshaft thread diameter of the O.S. FT-160 is 5/16", not 12mm. The FT-300 has a 3/8" propshaft. Both engines have a 24 thread pitch. They are NOT metric.

The Great Planes reamer will work with both:

GPMQ5005 4-STEP STD PROP SHAFT REAMER US$11.99

These parts can be ordered through any hobby retailer who sells Great Planes kits and accessories.