O.S. No.7 Short Body Standard Glow Plug "Medium Hot"This is an O. S. #7 Glow Plug. Recently developed to focus on easier running at low and medium speeds, this plug is a slightly hotter heat range than the O. S. #8 plug. This plug is ideal for helicopter engines with superior performance around hovering RPM range, which is critical for smooth and powerful 3D and F3C type flight. Also great all around plug for most 2 stroke standard plug airplane, helicopter and car engines. Model Heat Range Description