Class 125 threaded aluminum flanges connect with low-pressure (100-299 psi) pipe. Threaded flanges, or screwed flanges, include threads inside the flange bore which connect to the external threads on a pipe without welding. These flanges typically have a raised, flat, or RTJ (ring-type joint) face.

Class 125 blind aluminum flanges connect with low-pressure (100-299 psi) pipe. Blind flanges, also called blank flanges, seal the end of piping systems or pressure vessel openings to test the flow of a gas or liquid. These flanges typically have a raised, flat, or RTJ (ring-type joint) face.

Class 125 slip-on aluminum flanges connect with low-pressure (100-299 psi) pipe. Slip-on flanges, typically with raised or flat faces, slip over pipe. These flanges are manufactured with an inside diameter slightly bigger than the pipe's outside diameter. The pipe slides through the flange and is welded on both sides.

Class 125 butt weld aluminum flanges connect with low-pressure (100-299 psi) pipe. Butt weld flanges, also called welded neck flanges, attach by welding the pipe to the neck of the flange, transferring stress from the flange and the hub’s base to the pipe. The inside diameter of the flange matches the inside diameter of the pipe. Butt weld flanges typically have a RTJ (ring-type joint) face.