Hello Rick! Well of course, it's the opening to get the "modified" vice grip in there to crimp. It's just a cheap HF pair I smoothed the top and cut-off a bit at the bottom so there is no chance they will hit the upper can. Handy because you can stage crimp, this way you don't bow out the crimp ring, normally about 3 passes. Think clock, 12-3-6-9, then 1:30-4:30-7:30-10:30. Also very noteworthy is I wrap ONE layer of electrical tape around upper can where it will contact sprocket hole, keeps from scratching the paint on can. It's such a nice fit two wraps of tape would bind it.