I read in the reviews it was a perfect fit for HD-668B, so I ordered them as well. I can assure you, they are not a perfect fit for it. It was a two person struggle to get them on, as they are definitely smaller than the original pads. I do not recommend them for the HD-668B. I haven't tried them on long yet, but they do feel more comfortable than the plastic ones that were on it originally. It's not over-ear completely, but neither were the original ones. For this price, they are probably great for the HD-681. If you're shopping for HD-688B, I suggest you look for slightly bigger, better fitting velour pads.