EVERYWHERE, and I mean EVERYWHERE - it's advertised/reviewed/advised/marketed that the 41mm bands and the 45mm bands are not cross-compatible. I've went to various forums, reddit, even asked some questions in Amazon's question section for this band. Every single person in every medium has said that the 45mm bands will not work with the 41mm watch. Being the "Show Me Stater" that I am, I decided to see it for myself and ordered a 45mm band for a 41mm watch.I can say with 100% certainty (photo evidence as proof), that the bands are not limited to the case for which they were "intended." However, the band's attachment section is wider for the 45mm (1.375") and narrower for the 41mm (1.25"). Honestly, shame on Apple for making two different versions of the same product - it really makes no sense. The band should be the same regardless of the case size. Does it provide a functional difference? No. Will you notice the overhang of a 45mm band on a 41mm watch?Not if you use a bumper case like I do.I digress.The bands designed for each case size (41mm or 45mm) will work between both cases. You can easily use a 41mm band with a 45mm case size, or a 45mm band with a 41mm case size.In my particular situation, I am doing the latter: using a 45mm band with a 41mm case size (series 7).Why? Well, I prefer a smaller watch face. I work with my hands all day. When I don't work, I'm coaching, swimming, running or biking. And, I bump my wrists frequently.My wrist is 8.25" in diameter and while the 45mm watch with the M/L strap out of the box would have fit and been cheaper, I gladly paid more for a second XL band in order to have the smaller 41 mm watch face with a larger strap. Ask any Ironman, triathlete, swimmer, cyclist, i.e., any endurance athlete: it's what we like to use. It's not uncommon to see men wearing the "women" watches - because they're always smaller and lightweight. Form and function - that's what matters.I can squeeze in to the 41mm M/L band that comes standard with the 41mm watch. But it's not comfortable. I have to use the last notch on the band and there's not much room in the slip after tucking the excess band. It pinches the skin on my wrist and pulls my hair.If I use the 45mm M/L band, I use the second to last notch and it's effectively is the same length as the 41mm M/L band, except there is more excess that can be tucked into the slip, which somewhat alleviates the pinching.If I use the 45mm XL band, I use the very first notch and have a boat load of excess strap to tuck. This is by far the most comfortable; there is absolutely no pinching of skin or hair and the excess interior band provides additional cushion from the outer band against the styloid process of my ulna (see the picture). It also raises the watch face more anteriorly, which means I don't have to turn my wrist as far to view the face.So what's the take home?Apple needs to put more money into the functionality of the design and provide more size options for something as personal as a wrist watch. And NO, political colors don't count.If you've read this and are also experiencing issues with the size of the band and/or don't want to pay $50 for the right size band (which is far more than the band is worth), look up OXWALLEN on Amazon. They sell a cheap, elastic band for $11 that will get the job done at a fraction of the cost if you don't need a sweat, chemical, or water resistant band. I intitally got that band and then realized it's completely useless when it gets wet. I only use that band when I know I'm not going to be sweating or getting wet.If you do need a more hardy band, then sadly Apple's band is the probably your best way to go. Aftermarket TPU bands are good, but they're not great against harsh chemicals and attract dirt. They also don't have the same premium feel as silicone, which would be the next best choice before Apple's proprietary band material.