An optronic coupler is a tool used by Starfleet engineers for repairs of equipment.

Miles O'Brien asked Nog for an optronic coupler while working on the plasma distribution manifold system on Deep Space 9, right before asking for the phase decompiler tool. (DS9: "Empok Nor")

Optronics
opti-cable • optronic coupler • optronic data core • optronic data stream • optronic emitter • optronic integrator • optronic pathway • optronic relay • optronic weapons array