HP 1660CP Series User Manual page 182

Probing
Assembling the probing system
Connecting the Grabbers to the Probes
Connect the grabbers to the probe leads by slipping the connector at the end
of the probe onto the recessed pin located in the side of the grabber. If you
need to use grabbers for either the pod or the probe grounds, connect the
grabbers to the ground leads in the same manner.
Connecting Grabbers to Probes
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