In my Drafting days we had battery operated erasers that did have different grades of replaceable eraser sticks that would work on paper or mylar but I haven't heard the term, Glass Fibre eraser before, in fact I can't seem to find out much about them here in the States. Could that just be a term you call them in the UK? If I remember correctly the replaceable eraser sticks back then were about 6" long.
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