Dual electrode spark plug and gap setting

Manual calls for dual electrode spark plug. I find none for sale, and the Denso model number the manual references is a single electrode plug. Why the discrepancy? Are two electrode plugs still available? As to gap setting, the manual calls for.31. In your YouTube video you state the setting should be.44. The Autolite Iridium plugs I purchased are also set at.44. Is the manual stating.31 because it expects a dual electrode plug, or is that indeed the correct gap for any plug?