This is a Muffler Header for Top Flite In-Cowl Muffler. FEATURES: Provides the tightest possible in-cowl installation. Designed for use with O.S. 61SF and 61FX 2-stroke engines. ****NOT for 91 sized 2-strokes w/ TF muffler (too restrictive)**** INCLUDES: One Exhaust Header One Silicone Coupling SPECS: Header: 2-3/5" Long ½" Wide Length of exhaust opening at engine 1" Height of opening at engine 3/8" Distance between mounting hole centers: 1-11/16" Silicone coupling: 1" Long 9/10" OD REQUIRES: TOPQ7915 In-Cowl Muffler for Top Flite P-40 and P-51 Gold edition. ALSO 3.5x50mm or 6-32x2 screws (or use screws supplied with engine) COMMENTS: This also works for the Magnum .65 engine and the O.S. .60FP engines. DO NOT attempt to use this header/muffler combination js12/8/93 on the 91FX. ir/jl This header will also work with the .75AX (OSMG0575) 9/9/8 GX This will also work with the .65AX ABL (OSMG0558).