And I promise you, the Fat Bob is also a wide primary.

 

Yes, it's an old thread, but there's been a change, so for purposes of anyone searching in the future:

For 2018 the Fat Bob's primary outer cover was part 25700717. For 2019 and later, that part has been replaced with a narrower cover, 25701043. That part is available for installing on a 2018 bike. Same for the Heritage, 2018 had one primary cover, but 2019+ have a different one.

As to the definition of "narrow" or "wide", it is my understanding that the only bikes that have the "wide" inner primary cover are the Breakout and Fat Boy. The Fat Bob uses 36500104, which is shared on the other forward-control models, the Deluxe, Heritage, Sport Glide, and Slim. The mid-mount peg bikes use 36500105 (Street Bob, Standard, and Low Rider/S/ST). I THINK the only differences there are the finish (chrome/satin/gloss black/wrinkle black etc) and the presence of the hole in the mid-mount bike's primary covers to facilitate the mid controls.

Apparently the 2018 model year was a unicorn, having a narrow inner primary and at least some of the bikes having a wider outer; not even sure which ones fully qualify as "narrow" and which as "wide". For 2019+ I THINK that it's safe to say that all the bikes are fully narrow except the Breakout and Fat Boy.

 

If you're able to access the transmission shift lever and remove and replace it without needing to remove the inner primary, you've got the narrow one.