Says 5Z3 on the base,,, https://frank.pocnet.net/sheets/021/5/5Z3.pdf
The 5Z3 base is just an other tube visible in the picture. The 5Z3 is a 4 pin base.The tube he is asking about is an octal.
Put the tube in the freezer for a few minutes and when you take it out check on the side for the tube designation. You only have a few seconds when the numbers will be visible.