Rule of thumb if you are mainly doing commercial work, i.e. light weight / low pile, carpet base etc carpet, then a single puller is sufficient 90% of the time or more. (You can always pre-bevel the thick stuff to bind it easier). If you are doing mostly residential plush and berbers maybe 40-50 ounce and up, then a double puller will track through these rugs more easily and also help keep the work more square on the way through. Using a wider 1-1/4” binding tape will also help when binding heavier rugs as it allows us to open up the mouth of the tape folder and gives you more tape to reach around the carpet edge getting the stitch deeper into the carpet and away from the edge. Happy Binding!