The 4 setscrews secure your tool bits. There are some marks on the milled flat where you tighten your tool holder screws against the flat.I took some approximate quick measurements... They may be off a thousandths or two.
Also the Kennametal brazed on carbide bit shown in the photos is NOT INCLUDED. This one would fit in a 2 boring bar holder or lathe tool holder. It uses 3/4 HSS or brazed on carbide tool bits. Bit is secured by up to 4 setscrews.It is 20 long overall. Shaft is 15" long x 1.936" diameter. Tool holder head is 2-1/2" diameter x 4.725" long. The item "LARGE Lathe Boring Bar 2 Shank 2-1/2 Head 20 Long with 3/4 Bit Holder D412" is in sale since Thursday, March 26, 2020. This item is in the category "Business & Industrial\CNC, Metalworking & Manufacturing\Metalworking Equipment\Other Metalworking Equipment".
The seller is "hollowpoints" and is located in Uhrichsville, Ohio. This item can be shipped to United States.