A micro-spanner was a piece of technology used for repairs.
In 2153, Lieutenant Malcolm Reed asked Andorian Lieutenant Talas to hand him the micro-spanner while he was working in engineering aboard Enterprise NX-01. Talas told him that she brought equipment much more sophisticated from the Kumari but handed him the spanner. (ENT: "Proving Ground")
In the props requirement section of the call sheet for the first season episode "Civilization", a Micro-spanner is listed. However, the tool which Trip Tucker used as a lock pick does not match the micro-spanner seen in "Proving Ground".