Thanks for contacting National Instruments.
You really have two choices in connector blocks: the SCB-68 and the CB-68LP. The CB-68LP is inexpensive, but unshielded. If you are concerned about introducing noise into your signal, or if you are talking small measurements (mV range), then the shielded option, the SCB-68, will be better for you.
Regards,
Mike G.
National Instruments Support