Rens 1374d tube

Anyone have a slight idea about the Rens 1374d tube. This tube i have is a b4 socket, not the az1 series. Need to know what the side screws on the tube base is for. Any help would be great. Thanks!!
very likely a pentode. screen connected at the side screw.
rens is a RundfunkEmpfängerröhre for Niederfrequenz mit Schirmgitter. I assume you can understand that amount of german ;)