Product review (3 stars): As described, but...
It was a T shaped attachment for the rail inserted storm door sweep.  Problem is, this one was nearly 1/4" and the channel in my storm door was a tad less than 3/16".  I had to carefully trim it to fit which took much longer to do than it did to install it once trimmed.  It works though.  Dimensions of the "T" should be listed in product description.