B503 B50K RV16mm flat foot with switch potentiometer radio potentiometer.
I was desperately looking for such kind of potentiometer. I gave a deep look at local market, but no more electronic shop work with this mini potentiometer for old transistor radios. Fortunately, I have found it on AliExpress. It was very hard to find an exact unit with 16mm of diameter but after some effort I found it. It is only a pity that the freight was so high, but there was no other option, because it was the only existing advertisement. I will now assemble it on the radio under repair and cross my fingers that everything runs fine. Measured, the 5 received units, presented values from 46.8 KOhms to 51.5 KOhms, what I understand that are a reasonable and accepted deviation.