The Tektronix 067-0538-00 is a 20 pF input normalizer with BNC connectors.
067-0538-00 Top View
067-0538-00 Bottom View
067-0538-00 Female End View
067-0538-00Male End View
Tek 067-0537-00, 067-0538-00, 067-0539-00, and 067-0541-00