I am using these tubes in a 451 front recumbent wheel. They are supposed to fit both 406 (BMX-sized) and 451 (slightly larger) wheels. Installation into a 451 wheel is a little tricky because you need to stretch the tube to fit. Other than that, great tube, no issues. I've always been fond of Conti tubes.
It was easy to get the stem off and add slime. After repairing the front tire my son we out for a ride and rode over goatweed thorns sticking to the rear tire. I am glad that I purchased a couple of extra tubes. With the slime added they should last a long time.
I regret to say that these tubes, while solid in every way, have a poor fitment in my wheels. I purchased the smallest size for an ISO406 rim and found the tubes to be greatly oversized in their diameter. I packed these in the rims and spaced them out as even as possible and still have creases or folds in 3 or 4 spots on each wheel. I am disappointed with the fitment and will not be surprised the first time I get a pinch flat, but I will have a few months until the snow melts before I can test these guys out to determine whether that will truely be an issue.