There are several types of connections used for steel angles in steel frames, including welded connections, bolted connections, and riveted connections. Welded connections involve fusing the angles together using heat, creating a strong and permanent bond. Bolted connections involve using bolts and nuts to secure the angles together, allowing for easy disassembly if necessary. Riveted connections involve using rivets, which are metal pins, to hold the angles together by forming a permanent, tight fit. The choice of connection type depends on the specific requirements of the steel frame and the desired level of strength and durability.