loop, loupe

Loop or loop means a cord or string turned around and crossed over itself, leaving a teardrop or circle shape--
Make a loop and tuck one end under the other.
Make one end of the shoelace into a loop, and wrap the other around it.

Loupe or loupe ( rhymes with loop ) means the eyepiece that a jeweler uses to magnify gems and jewelry--
The jeweler used his loupe to find out if the gems were real.
I can't read the marking on this silver. The jeweler will be able to see it with his loupe.

Now that you know that, you can say--
"I would need a jeweler's loupe to repair the fine gold loop on the end of this chain."

Note--a "loophole" is a small opening, and is often used in a figurative sense--
He hoped that a lawyer would be able to find a tax loophole for him.

Note # 2--"loopy" is old-fashioned slang for crazy, dotty, or pixilated--
Wally and the Beaver didn't want to play with the loopy kid next door.