This is a 1/2" muffler extension for .40-.46 size engines such as O.S. MAX, ASP, Magnum and Thunder Tiger. This goes between the engine and muffler, bringing the muffler outside the fuselage. INCLUDES: (1) 1/2" aluminum muffler extension (2) 3 x 50mm cap head screws JAL 11/15/95 COMMENTS: This extension will fit any engine that has the same exhaust port dimensions as the O.S. .40-.46 SF engine: ASP .46, Royal .46, Thunder Tiger Pro .40-.46, and the Magnum XL .40-.46. SPECS: Distance between centers of mounting holes: 36mm(1.419")(about-1-3/8"). Exhaust port dimensions: 30mm(1.184")(about-1-3/8") x 8mm(0.321")about-5/16" JCT 10/10/01