An object of the present invention is to provide a spark plug which has more excellent impact resistance with electrical conductivity and airtightness kept excellent. When said heat treatment jig is used, generation of a slip can be prevented during heat treatment. A valve coupled to the first instrument controls fluid flow through the first channel, such that impedance of fluid flow through the first channel is substantially the same without the second instrument received in the first channel and with the first channel partially blocked by the second instrument. In the second mode, a program that has been reproduction restricted is prohibited from being reproduced. In accordance with another aspect, a keying system is providing including a key member for engaging a connector and a complementary key member for engaging a electrical plug.