STD-2180 Hose, 3/8 ID x 1-13/16 long.
Download the diagram (PDF)
Note: The part number in the diagram is No.2 part.
The 3/8 x 2-1/2 Lycoming part # is STD-1821
Thats because you didnt do enough research, this isnt the right return hose for your engine...
The original hoses that came off my Lycoming are 2.5 long. These new Superior hoses are only 1.75 long... they are too short and work.
This hose is made from oil resistant neoprene Buna-N.