This is a just a nut III. Plastic Warwick nut off of my Thumb 5. Standard 5 string spacing. B string and maybe the E looks like it was filed down some, but still plenty of room with the adjustment screws to fit any bass $35 shipped
they may be. I’m not the original owner, so I have no idea. I personally have not done any filing. But the action of the bass was spectacular.
Of course, I didn't even think to suggest that you have done it. It looks to me that the nut was used on a quite smaller fretboard radius than warwick which is somewhere around 20" depending on the german made vs rockbass.
from what I understand, this nut was original to the bass which was a 1998 Thumb 5 BO. But again, no way to confirm.