Pico D9 to Dual BNC Adaptor The TA299 is an optional accessory, and a useful adaptor to have in your kit. The D9 to dual BNC adaptor allows you to make differential measurements using two single-ended probes with BNC connectors or connect two BNC cables from custom hardware. The PicoScope 4444 will identify the TA299 adaptor but not the probes connected to it.