I have an old pair of secondhand clippers, very heavy and big,There are no markings on them to say what they are, nothing to say what wattage etc. They have a green body ! someone has said they think they are Lister, I am using WOlsey A6 blades on my wire wool cobs legs. I cannot seem to get the tension right, there are no markings on the tensioning screw either ! Anyone got any ideas