The B8A base is found on valves in the UK that date from the late 1940s and very early 1950s. The all glass B9A and B7G displaced the B8A base. We do not have exact dates as yet for when this base was current technology but B8A based valves first appeared in the UK at the National Radio Exhibition in 1947.
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.
The problem with hard pins is that any force applied to the pin is likely to cause a break in the glass base. Later all-glass bases such as B7G and B9A valves used softer pins that bent rather than breaking the vacuum seal.