You're probably thinking the #13 blade. It's rated to maybe thin roofing metal, and that's about it, and only for a short time. I think it was probably really ment for softer, copper-based alloys in making various crafts. <br><br>The #15 and #27 really aren't up to being used on metal, but they are longer and work on light woods and plastics. <br><br>The #26 whitting blade might be perfect for PSK use.<br><br>For those who are interested, <br>http://www.einsteins-emporium.com/col-supply/x-acto/ctx10.htm<br><br>http://www.x-actoblades.com/xacto/xpage1.htm