MSO 70604C threaded input interface

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?
 

Hi Eric,
 

The ports on the MSO70kC are TekConnect ports.
 

TekConnect to BNC or SMA (both 50 ohms) adapters are available here: https://www.tek.com/en/datasheet/tekconnect(tm)-adapters