I bought these on the recommendation of a friend who is known in the community for his woodwork experience. I was in the process of making small bookshelves when I got them and what usually takes 30 minutes one shelf and yells at my 14 year old boy to keep the board straight ended up having the entire bookshelf done in 30 minutes. lots of time for me! If you're building something that requires a 90 degree angle, this is a must!