Our standard and angled premium high-density bone nut found on all models. String grooves are guides and available on standard nuts only . They are not set to depth. Some Adjustment will be necessary for proper height and fit for all nuts. Larrivée recommends installation be done by a qualified technician. Angled nuts are for 40, 44, 50, & 60 Series only, come in one size, and are not pre-slotted. Contact Larrivée Service if you require assistance.