The NID barrels I pictured are from a No. 4E two-barrel set. The 4 on the left barrel flat, to the right of the serial number is the grade. The choke markings are at the front of each barrel flat. 4 & 4 for full and full and 1 & 1 for improved cylinder and improved cylinder. The + marks to the right of the choke marks are the mark of Charles August the worker who proofed the barrels.