This tool will fit Renogy and Bouge RV MC4s but not HQST. The round nut is the most diverse. The plastic key round nut is too small for HQST MC4 connector but fits Bouge RV MC4 very well. In the center of the key is another hole in the shape of a rectangle with a circle in the center. This part was also very difficult to install on the HQST MC4, but fitted the Bouge RV and Renogy MC4 very well. I bought a Renogy crimp for the MC4 and it seems to work fine for these connectors as well. I don't blame the tool maker for the fact that MC4 connectors seem to vary from brand to brand, but I thought this detail was worth mentioning. The tool was released under the Renogy brand. So if it doesn't match the HQST branded MC4 then it really shouldn't be considered their problem. Again; it fits very well with Renogy and Bouge RV plugs.
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