Peter Buck

The specifications of a custom string set "w[ere] posted to the alt.guitar.rickenbacker Newsgroup in April 1999", as reported and preserved by RickResource. "Nickel Steel Electric" is also listed on REM's official Dean Markley artist page from 2005, while a heavy gauge is noted by REM bandmate Mike Mills in a Bass Player interview published to Guitar World's website on November 11, 2023.

RickResource

There was a question awhile back about what type and gauge strings Peter Buck uses on his Rickenbacker 360 Jetglo. This response was posted to the alt.guitar.rickenbacker Newsgroup in April 1999. It's a rather heavy set consisting of:

1st - .013 Plain- Swedish Steel

2nd - .017 Plain- Swedish Steel

3rd - .026 Wound- Nickel Steel

4th - .036 Wound- Nickel Steel

5th - .046 Wound- Nickel Steel

6th - .056 Wound- Nickel Steel

These are Dean Markley individual strings. His guitar was at the factory so that he could have a new instrument set up exactly like his old one, using the string set listed above.

Dean Markley Artist Page

REM uses Nickel Steel Bass Med. Lt, Nickel Steel Electric, and Vintage Bronze Med. Lt.

Karl Coryat, "'Early on I discovered that the bass player decides the chord – not the guitar player': R.E.M.’s Mike Mills on finding the perfect bass part and becoming a 'one-bass guy'", Bass Player via Guitar World, November 21, 2023

When you play guitar do you think of Peter's style?

“I try not to, because that would defeat the purpose. For one thing, he uses very heavy guitar strings, which I can't really handle. I could never even begin to play like Peter, so there's no point in trying – although his guitar playing has influenced mine to an extent. It’s more subconscious than conscious.”

Listed on REM's official Dean Markley artist page from 2005.

REM uses Nickel Steel Bass Med. Lt, Nickel Steel Electric, and Vintage Bronze Med. Lt.