The TO-92 package is normally a three terminal plastic transistor package. However, Littelfuse modifies this package by trimming the center lead short. As such, it serves as a stand off to assure the TO-92 is inserted to the correct depth on the printed circuit board. TO-92 devices all contain a single SIDACtor chip and use the package designation “E” in the part number. The DO-15 axial package may contain one SIDACtor chip or a stack of two SIDACtor chips. This package is footprint compatible with many leaded gas tube devices. All axial SIDACtor devices use package code “G” in the part number. The TO-220 package, with its mounting tab, is only used for the 3000A SIDACtor device family. Note that the mounting tab is connected directly to the center lead. Littelfuse calls this package the “R” package. The modified TO-220, which is called the “A” pack, can contain one, two or three SIDACtor chips. The modification refers to the missing mounting tab so that the body of the package is completely covered in epoxy. The TO-218, or the “M” pack, is the largest package and is only used to house the 5000A SIDACtor family. Like the TO-220 package, the mounting tab is connected to the center pin, however this pin is not connected to anything inside the package.