The relaxation was to clear hardness caused by the induction hardening of the rear locking lug. There was no hardening at the front of the body. I was also told at H&H that a rear pad could be moved slightly to cater for uneven machining of the locking lug recess, where it mmight shallow and give insufficient thread. Whether THAT explanation - after 50 years had morphed into the actual explanation of the slight spread of the induction hardeing of the shoulder, nobody knows now. But there certainly was a relaxation/ And .060" seems to spring to mind