The Kuryakyn part number is #8309 and is called: Vented Flush Mount Gas Cap. It initially was designed for right hand thread HD models. It comes with a couple of gaskets. Any will work, but the largest one allows the cap to sit more flush in the dash.
It has been reported that this cap will not fit some 06 and all 07 and 08 models due to tighter neck threading. I suppose there was a template or die change. Mine is an 05, it fits great and I love it.
