Block Style Flex change letters are the second most popular of all flexible plastic letters on the market.8? Printed Black Letters/Red Numbers on 9-7/8? Clear Background plastic Font Count: 290 These letters should not be used on signs if the letters are encased within a wind or vandalism cover. Portable sign letters are thin and bendable from one end to the other. These will NOT replace the thicker "RIGID" marquee letters. These are not replacements for Rigid, Gemini, or Zip letters. The track used by rigid type flat letters is called "Push up drop-down track."