An external clamp, or outer clamp, has a simple structure but essentially performs the same function as an internal clamp—that is, aligning and joining two pipe ends for welding operations. In certain cases, however, it becomes necessary to use the external clamp instead of the internal one. This is especially true during repair work, pipe modifications, or when making connections where the internal clamp cannot be removed from inside the pipe. Internal clamps are typically made in two types: screw-type and hydraulic jack-type. Screw-type clamps are usually used for smaller pipe sizes, ranging from 6 inches to 24 inches, while jack-type clamps are suitable for larger sizes, from 24 inches up to 56 inches.