APT Precision Boring Head - Overall Length : 3-3/16" THREAD BACK: 7/8"-20 Offset: 3/4" Go to amazon.com Related posts Expert choice for boring head set FeatureDirect reading .001" micrometer dial.Precision hardened steel.Boring capacity: up to 4" holeHead Diameter: 2-1/2"Hole Diameter: 1/2" DescriptionVertical Hole Spacing: 3/4"