Hello again from ForeverHandCrafted!  We're very happy to offer our slotted Cow Bone nut for Martin guitar in the 45mm / 1 3/4" length.  Some Martin acoustic guitar models use a 1 3/4" long nut.  We make this item in our Michigan shop from pure white Cow Bone blank.  Beautiful satin polish finish.  Shipped to you immediately with full postal tracking.