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help with roller! need help asap

i built a vdg and it works. but since the top roller is AL all it does is produce static electricity until it sparks to the AL on the roller. instead of going to the dome. i have to present it at science fair so i need another roller. i was thinking nylon. so i bought a bed frame roller wheel. but i dont know if it is nylon. so does anyone know if there is any thing i could use that would be at hardware stores or any stores?

Is the roller inside the dome?