The B8B, or Loctal, base was developed by Sylvania for use in car radio equipment where the positive locking in of the valve with the spigot provided a more secure fixing than the RCA International Octal, IO, upon which it was based. The Loctal base came into use in America in 1939. This base was mainly used by Sylvania and Philco. The first use in the UK was in 1947 when B8B valves appeared in the UK at the National Radio Exhibition in 1947. The B8B was at the time described as similar to the Loctal base.
On the whole the B8B range of valves was not a long-term success. The pins were extensions of the Fernico metal used inside the bulb and as the valve-holder used a different metal, corrosion of the pins resulted leading to intermittent contact. The Loctal base was knocked sideways by B7G and then annihilated by B9A before really gaining a market niche.
The pins are hard and inside the envelope they provide the supports for the electrodes. As the pins are equi-spaced around the circumference of the circle, a locating spigot is required to provide a positive registration with the socket.