The 3AFP31 is a high sensitivity green screen oscilloscope tube. The P31 denotes the phosphor colour. For a tube with a small screen diameter it is quite long, and it is this shallow deflection angle that enhances the deflection sensitivity. The screen is 68 mm in diameter.
The electrodes are held in glass rods and the gun is held in place in the envelope by the springs that can be seen on the right. The flaring deflection plates on the left are the Y plates. These are always closest to the gun as that is where the sensitivity is the greatest. The hollow cylinders to the right of the picture are the anodes.
Another view of the anode cylinders, fixing springs and Y plates. The pattern stamped on the deflection plates is there to make a thin metal sheet more rigid by introducing small corrugations.
The end window envelope is 40 mm in diameter, and excluding the B9G base pins is 232 mm long.
Reference: Data-sheet. Type 3AFP31 was first introduced in 1960. See also1960 adverts.