This is a In-Cowl .61-.75 Muffler for the Top Flite P-40 Warhawk, P-51 Mustang and AT-6 Texan. FEATURES: Completely Conceals Inside the Cowl Bolts Directly to the Firewall for Maximum Security Can-Type Cylinder For use on .60-.75 2-Stroke Engines. ** NOT FOR .90 OR LARGER ** INCLUDES: Muffler, Firewall mounting screws (2), Pressure fitting, Pressure Fitting Gasket, Silicone Mounting Washers (2), Pressure Plug Screw. SPECS: Muffler- 3¼" Length 1 9/16" Diameter Exhaust Port- ½" OD ¾" Long (2) Silicone washers- ½" OD 3/32" Wide (2) Wood screws- 20/32" Length Pressure fitting- 6-32 Threads Pressure fitting gasket- ¼" OD 1/32" Thick Pressure fitting screw- 6-32 Threads REQUIRES: TOPQ7920 O.S. exhaust header for .61 SF or FX 2-stroke *** not for use on ST90 or OS91 2 stroke engines.*** JS 12-8-93 The muffler is too restrictive for ANY 90 sized ir/jl engine and will cause overheating problems. SuperTigre exhaust header for G75 COMMENTS: Don"t use this one with OS 65AX engine, it doesn"t have exhaust header, which is not available separately. Instead, use TOPQ7920.