Angle Blocs are a tricky but rewarding type of hold. They are best used as foot holds on slabs or hand holds around aretes or on vertical walls, because when you move over them, they become useless. This makes them great for technical problems, where you need to use your feet and hands carefully to stay in balance.
Angle Blocs are available in a variety of colours, so you can choose the ones that best match your wall. They take 50mm bolts, but you will need to purchase these separately.