Eric Prechtl

We have a MSO 70604C oscilloscope.  We need to take a measurement of a relatively fast set of signals (~180 MHz) and we'd like to use the 50 Ohm termination of the oscilloscope.  We only have TCA-1MEG input amplifiers.  So we need to remove those amplifiers and engage directly with the threaded input into the scope.  They look like they have a thread with a major diameter of about 0.375 inches (much bigger than a typical SMA type connector).  Can anyone tell me what threaded interface these ports use?