Impact works best here, or if its the old strut you can try a vice grip on the shaft, but I've never had any luck with that approach. The star nut comes off easy with a few taps, but it needs to be tight after reinstall with new struts. I suggest re-installing on car with out top cap and "making" a 4 slot tool from a harbor freight impact socket. Blip it a couple of time with the impact gun to make sure its tight, then spin on the top cap and nut. You should be good to go. good luck.