1/2" grommets, but use rubber padded wire so little thicker. I got like 3-4 per grommet then I use tied down branches to attach branches from above, just to tight to work in the thick lol.@Mcdee -- can't believe you ran out of grommet space, you made 'em big enough to handle multiple attachments, I thought. Like you, I've always been rewarded by training. Slowly migrating from clothes hangers, pipe-cleaners and flexible rubber wire to more high-tech (and pricey) tools. Been playing with a set of Atlas Plant Trainers for a couple of grows. Very useful when plants get large and wide. Now looking into Stem Trainers for more modest LST work. :smoking: