A great, rigid and lightweight stock - DoubleStar ARFX AR-15 Skeleton Stock

Yes, the foam tube is difficult to slide over your buffer tube. I used a can of compressed air of the sort used to clean computers, inserting the thin tube under the foam tube and squirting air while tugging the foam toward the receiver. The round locating stud is a tight fit in its corresponding hole, but it does fit. Be sure it's aligned, then use the supplied flathead machine screw to snug the stock into place.
The stock is light and rigid, and inspires confidence where rattley adjustable stocks do not.