what is a soft gummi stone to be exact? i know i need one to detune my tail and tip, but since i've never seen one i dont know exactly what to get. the ski shop in my area doesnt have any, but they say i can get one from a hardware store. i looked at ace, but i didnt see any. would they be called something else at the hardware store? all i saw were stones for sharpening knives. is it really soft? or is it just a stone?