The product I ordered (Singer Futura 1050 hook gear) fitted like a glove, using cold on axel and 80 degrees C heat. The pinhole on the new cog was very lightly off, but could insert the pin anyhow. It was possible to fine align the cog using locking pliers even after the fitting. Oh, and the removal of the old, broken cog: just hacksaw. This is for anyone wondering, non-professional like me.