I thought I read somewhere they were Elixers , but the balls are red, black blue gold so maybe D'Addario. Just been NBD'd with a SR500 - these round came off the same day for TI flats. These are still 'sticky' so need a bit more playing in.
Interesting comment on their website about the Bartolini Mk1 "Like traditional single coil but without the hum". They are actually P type pickups under that cover, but reversed compared to a P - treble side nearer the neck.
I think I preferred the P/J pickups on the cheaper SR200, which this replaced, but I'm still fiddling with the pots. The price drop of the SR200 was one reason I upgraded
songofthewind - if you need a spare set of rounds, you can have the ones I took off, never been played. They will go back on if you don't twist them. Nice slots in the bridge unlike BBOTs.