This is what we found on Wikipedia regarding the Steph Strings:

Stephen "Steph" Carpenter (/ˈstɛfən/ STEF-ən; born August 3, 1970) is an American musician, known as the co-founder and lead guitarist of the alternative metal band Deftones.

His guitar technique makes use of both ringing open strings and dissonant chord voicings, as well as stock power chords in polyrhythms. Carpenter began his musical career with Deftones playing the traditional six-string guitar. After becoming influenced by such bands as Fear Factory and Meshuggah, he began playing a seven-string guitar in the late 1990s. After Deftones' third album White Pony, subsequent releases would be written with seven-strings, until 2010's Diamond Eyes and 2012's Koi No Yokan, which were written with an eight-string guitar. Starting with 2020's Ohms, songs have been written with nine-string guitars. Carpenter was ranked 60th in Guitar World's The 100 Greatest Metal Guitarists poll.