Most tube sockets can be mounted using #4 size screws and nuts or #4 self tapping screws.
I stock screws and nuts on this pageSee this document on how to mount tube socketsPlease install all tube sockets with a tube in the socket.
The pins on the socket will not be lined up correctly if you do not have a tube in the socket while soldering them.
It may be very difficult to install the tube if the pins are not aligned properly and you may damage the tube socket pins.
Bias checkers have been moved to the Tools page