On the wall in the living room of Leonard and Sheldon's apartment is an antique fuse holder with fuses.
This odd item was the subject of much discussion by fans who couldn't work out what it was. Eventually, someone identified it on Twitter.
Here's the link of Big Bang theory wiki page.
Look closely, each row has a fuse connected from the left to right. Each fuse is bolted to it's connection on the terminal block with two bolt. Each fuse has two eilets (one on each side) where it is bolted onto the terminal block (or strip).
Give a look here
Here's the photo linked there: