Butt splice connector to join 10 gauge to 12 gauge wire?

Yes, the 10/12 means the connector can be used for those gauge sizes.

However, do not use these



to make the crimps.. Pliers just smash things and the result is a very lousy connection that will fail quickly..

Instead use one of these if you must crimp..



Found HERE for $12 Have never had a crimp made with that tool fail.

Have however had to fix a lot of failed crimps that folks used pliers on.