Magnifying eyeglass
A magnifying eyeglass was a type of monocle that could be worn on one's head, which  functioned like a magnifying glass.  

In 2370, Elim Garak used a type of eyepiece while repairing a computer at the Tozhat Resettlement Center on Bajor. After he was able to bring the computer online, he handed it to Julian Bashir, who inquired about the tool, "You carry this everywhere, do you?" Garak acknowledged, stating plainly that it was "[a] simple tailoring tool," adding, "[y]ou'd be 
surprised how often someone needs a pair of pants let out..." ()

Tools