I've seen that type of extension. The one I saw belonged to my grandfather. He was disabled, and could not seat "correctly" in a standard automobile seat. He had Scoliosis and did not sit "straight" in any seat/chair. He had an extension that was similar to this (his was for the 80's Chevy Belts) that with this extension, allowed him to better position the seat belt for comfort/safety, since we wasn't where the belt was designed to be used. I believe they could also be acquired for those, as stated above, are well nourished. However, I am 6'4" and 350+ lbs, and I personally have not had an issue with fitting any seat belt, as supplied with the vehicle. There have been a few that have not had a whole lot of slack once fastened, but they still fastened and worked fine.