I bought a set of these clamps for a neighbor who has woodworking experience in our community. I was in the process of making small bookshelves when I got them and what usually takes 30 minutes one shelf and yelling at my 14 year old boy to keep the board straight ended up having the entire bookshelf done in 30 minutes. The orange arrow slips when I use two different sized pieces of wood. The gray covers slide up and down as needed when I use 3/4 plywood for both parts of the clamp. These brackets saved me a ton of time! If you're building something that requires a 90 degree angle, this is a must.