In electronics, TO-5 is a designation for a standardized metal semiconductor package used for transistors and some integrated circuits. The TO element stands for "transistor outline" and refers to a series of technical drawings produced by JEDEC.
The typical TO-5 package has a base diameter of 8.9 mm (0.35 in), a cap diameter of 8.1 mm (0.32 in), a cap height of 6.3 mm (0.25 in). There exist variants with from 2 up to 10 pins. The pins are isolated from the package by individual glass-metal seals, or by a single resin potting. Sometimes one pin is connected directly to the metal case.
There are multiple variants that differ from the regular 3-pin configuration. The H06C variant with 6 pins has its marker between pin 1 and 6, and H08A has 8 pins with the marker on the last one. The counting order is clockwise from the bottom perspective.