<Tr> <Td> 2PP </Td> <Td> Two pin prefocus </Td> </Tr> <Tr> <Td> 3P </Td> <Td> Three prong </Td> </Tr> <P> Some of the above base styles are now obsolete . The trend in recent years has been to design newer bases to reduce waste of raw materials and simplify the replacement process . </P> <P> The United States standard for lamp sockets is published by ANSI and developed by NEMA . It is standard number C81. 64, titled Guidelines and General Information for Electric Lamp Bases, Lampholders, and Gauges and outlines the dimensions and tolerances of standardized lamp sockets . Lamp bases are standardized in C81. 61 Standard for Electrical Lamp Bases - Specifications for Bases (Caps) for Electric Lamps . Both standards are harmonized with IEC standard 600061 and include dimensional data sheets as printed in the IEC standard . </P>

What is the difference between light bulb bases