I've been using ramps for about eight years, I usually just make them myself out of ebony, or rosewood, I works great to keep your fingers from getting under the strings, Gary Willis first came up with the idea on an early tobias, There were ten pre-gibson tobias made like that, I owned one, It was one of the better basses I've ever played. You want the ramp to be radius to match the fretboard so the height is consistent across all the strings. Good luck, B