This is an alloy steel seal plug - a stepped body with a sealing nose that carries a couple of O-ring grooves, and a 1/2-13 UNC tapped hole down the base to pull it. We turned the steps, the radiused shoulder and the grooves, then drilled and tapped the centre. The O-ring grooves have to run smooth for the seals to seat, so we held a 63 Ra finish in the grooves. Straightforward turning, but the seal surfaces are where you don't cut corners.

Material: Alloy Steel (chromoly) | Operations: Turning, Drilling, Tapping | Size: around 4-1/4" long, ~1-7/16" OD | Feature: stepped sealing nose, O-ring grooves, 1/2-13 UNC tapped base | Finish: 63 Ra in the O-ring grooves