The Phonak Power SlimTube II are for use with Phonak BTE hearing aids and a custom earmould - a dome will not fit on a Power SlimTube II.
Phonak Power SlimTubes have a 'female' thread fitting onto the hearing aid. The thread is slightly larger than a Power SlimTube and has a cross slot for a tamperproof pin if required. They are marked at the hearing end with a number indicating the size in red (for right) or blue (for left).
Phonak Power SlimTube II fitting guide