Sorry it's an Opto Isolator.

"The Opto Isolator Unit is designed to electrically disconnect and isolate all servos and their associated wiring from the receiver, thereby removing all radio frequency interference entering the receiver via the servo connections. The use of this unit has several other benefits including improved receiver operating range and the possibility of running the servos and receiver on different supply voltages. The unit is supplied with eight short fly-leads fitted with universal plugs for connection to the receiver and eight standard pin connectors for connection to the servos".

This is from SM Srevices

http://smservicesuk.co.uk/acatalog/L...del_Units.html