Both the single-action compression truss rod used between 1980 and mid-2006 as well as the non-compression truss rod used between mid-2006 and mid-2013 have a separate truss rod nut. The pre-2006 bullet nut has imperial dimensions and needs a ⅛” hex wrench. In the early days, this bullet nut was about .992” long with an outer diameter of .358”, and usually stuck out quite a bit as seen below on a 1980 L-1000 and an F-100 Series I from a year later. Of course this was not possible for any guitar with a string locking mechanism at or behind the nut, as for this 1985 Rampage. In those cases, it might even be hard to find the nut! Some of these deep seated nuts seemingly found their way onto guitars lacking a string lock mechanism like this ASAT (low string tree) from 1989. Post-1989, the bullet nuts definitely did not stick out as much as before, as illustrated by the ‘Z-5000’ prototype or Lacewood Commemorative #1, both from late-1991. The latter even has a gold bullet nut. Sometime after BBE Sound, Inc. took over G&L, the nut became a little less domed with a more “squarish” top, i.e. about .983” long with a .353” outer diameter. Although with plenty of exceptions, it was countersunk rather flush with the end of the channel as demonstrated on this ASAT Special built for Guitar Shorty in 1994. This incarnation of the pre-2006 bullet nut is still available in the G&L Online Store. The post-2006 nut, as found in the same store, has a flat top, is about .977” long with a .314” outer diameter, and needs a 4mm hex wrench instead. Note both the bullet and metric nuts come with 2 brass washers having the same dimensions in both cases: .058” thick, .373” outer diameter and .200” inner diameter, The ASAT Classic ‘S’ from 2007 and 2016 SB-2T ‘Juicy Lucy’ shown below are examples with a metric nut. For the latter, the nut is actually welded to the dual-action truss rod and cannot be replaced. This change occurred in mid-2013 for US built models and mid-2015 for Tribute models.