Don't know. All I know is the Probucker 1 in the neck position on my 50's Standard sounds awesome. Much better than the probucker in the Plustop Pro I sold.I just noticed that the 2020 50's specs say Probucker 1 & 2. My 60's (and most of the others) have 2 & 3's. I can't find any info the 1 & 2's. Is this a real thing and, of so, what differentiates one set from the other?