They work well with Temco PV cable MC4 connectors, but not with Sunpower PV panels (flexible/portable) MC4 connectors (pins are too big to fit in to fit Sunpower MC4 connector holes). I sharpened the tines on a tool and it now works with the Sunpower MC4 connector. I now have tools for Sunpower and Temco MC4 connectors. Now they do the job with two tools (one modified). Please note that not all MC4 tools will work with some MC4 connectors.