- High Side R134a service port with 10mm switch port - Fits 3/16" Flare (3/8" SAE) R12 Service Port - Tee adapters should be used when there is only one high side or one low side service port on the vehicle and a switch port and service port are both needed for the R134a retrofitted system. - Tee Adapters can be used when there is an existing high side or low side switch on the original R12 system or if it is necessary to install a high pressure shutoff switch on the system.