Fischer elektronik transistor retaining fischer elektronik thfm 1 the fischer elektronik transistor retaining spring thfm 1 is a well designed universal retaining spring manufactured with stainless steel and equipped with quick and easy transistor fitting for housing to 218 to 220 to 247 to 264 sot 32 and various sip multiwatt fischer elektronik thfm 1 transistor retaining spring 1