male BNC to 5 mm scope probe adapter

[rocksam]

I see a lot of sources for a female BNC scope probe adapter which people use to plug their probe directly into the signal generator, but I prefer a male BNC scope probe adapter that I can use on a BNC "T" ehich is connected to a BNC 50 ohm feedthru to the signal generator. Years ago these were common in electronics labs, now they seem to have disappeared. There are some on ebay (Chinese) but they are 4.5mm for some reason I don't understand. Does anyone know of a source for a male BNC to 5 mm probe adapter?