Several Tektronix products use miniature coaxial BSM connectors – also sometimes called MB connectors – e.g. the 7D14, 7T11, FG501, 11B2, 3S2, S-50. S-51, S-52, and 067-0587-01. These look like minature BNC connectors.
There are two-lug variants and three-lug variants. Tektronix used the two-lug variant. BSM connectors are much less common than BNC connectors and are hard to find on the surplus market.
The Tektronix 012-0127-00 adapter cable converts from BSM to BNC.
BSM female on front lower right of 7T11
BSM to BNC adapters
BSM panel jack
BSM cable plug
BSM cable plug (right) compared to BNC (left) on 012-0127-00