omnigrid 4-6-12-inch marking ruler trio omnigrid omnigrid marking ruler trio are made from a durable premium quality plastic and laser cut for a smooth edge that allows for easier deeper cutting of fabric layers. designed for left or right handed use. use these rulers to quickly and accurately perform a variety of marking tasks. center line is exactly 1/4 from both edges of the ruler. do not use with rotary cutter knives or other cutting instruments. rulers are designed for marking only. includes 4, 6 and 12 rulers.