Quoted from MIL:BLACK_ROSE said:
Go to a Hobby store and get some Thin Felt and Glue it to the wood on the edge of yr P/F's Or you Will Scratch the Mirror Blades .. I know this already ...
Or you could buy some felt from here :
http://www.pinrestore.com/Supplies.html
( about half way down the page ... called self adhesive felt strip )
Comes in a few sizes .. get the super thin stuff . Works great . I have it on all my playfields , mirror bladed or not .
If you're doing a lot of games, this stuff is a fraction of the cost:
http://www.amazon.com/gp/product/B000QDRRNE/ref=oh_details_o04_s00_i00