All our toppers are tuned to work best with the heavy-duty green t-posts you’ll find at most farm supply and hardware stores. They seem to be readily available and the sturdiest t-posts we've found. They should measure about 1.25x1.30", not including the nubs. All our t-post toppers can still be run on lighter or off-size posts, but the hold may not be as tight, and we can’t promise top performance if the post isn’t up to spec. For the cleanest fit and longest life out of your gear, stick with the heavy-duty green fellas.