There are many types of reed relays. The contact configuration used for a given design or application is typically described by its contact form, such as one Form A, one Form B, and etc. Contact one Form A is a single pole single throw (SPST), normally open (N.O.) relay. Contact one Form B is a single pole single throw (SPST), normally closed (N.C.) relay. In the case of the form B switch, the contacts are initially held closed by an internal biasing magnet.