Lamp Guide: Incandescent by Brandy McNeilin GuidesFebruary 17, 2017 Incandescent Filament Designations Filament designations consist of a letter or letters to indicate how the wire is coiled, and an arbitrary number sometimes followed by a letter to indicate the arrangement of the filament on the supports. Prefix letters include C (coil) — Wire is would into a helical coil or may be deeply fluted; CC (coiled coil) — wire is would into a helical coil and this coiled wire again wound into a helical coil. some of the more commonly used types of filament arrangements are illustrated. C-2VCC-2V C-5 C-6CC-6 CC-6 C-7A C-8 2CC-8 C-9 C-11CC-11 C-13CC-13 C-17A C-2RCC-2R MP BP FF M SC CC-6 CC-8 Incandescent Base Types Incandescent Bulb Shapes The size and shape of a bulb is designated by a letter or letters followed by a number. The letter indicates the shape of the bulb while the number indicates the diameter of the bulb in eighths of an inch. For example “T-10” indicates a tubular shaped bulb having a diameter of 10/8 or 1 1/4 inches. The following illustrations show some of the more popular bulb shapes and sizes. A B BA A-19 A-21 A-23 B-10 1/2 B-13 BA-9 BA-9 1/2 BR C ER BR-19 BR-25 BR-30 BR-40 C-7 ER-30 F G K P F-10 F-15 F-20 G-16 1/2 G-25 G-40 K-19 P-25 PAR PS PAR-16 PAR-20 PAR-30S PAR-30L PAR-36 PAR-38 PAR-64 PAR-64 PS-35 R RP S R-20 R-30 R-40 R-40 RP-11 S-6 S-11 S-14 T T-4 1/2 T-5 T-6 T-8 T-8 T-10