Three HSS Boring Bars included Head Diameter - 1 3/4" Overall Head Length - 2" Boring Bar Hole - 3/8" Slide Radial Travel - 5/8 Minimum Bore - 3/8" Maximum Bore - 3 3/16" Mounting Thread 7/8 x 20 Graduated- 0.01". Soba 1 3/4 Boring Head Set with R8 Bridgeport Shank Ref. QUALITY TOOLS FROM CHRONOS - HUNDREDS MORE IN OUR ONLINE CATALOGUE. Create listings that get noticed! With Auctiva's 1,800+ Templates.