All the parts

Here's a shot of all the parts of the burner.

On the left - the burner body (red cast-iron)
Second, is what I like to call the air-flow regulator. It's the little plate that you turn to cut-off or allow more air to flow into the burner to adjust the flame.
Third, is the spring that applies pressure to the air-flow requlator so that it is held in place when you turn it.
On the far right, is the brass fitting. This is the part that you will be working on. There's two ends: One is the side where you connect you gas line. The other is the orifice that you will be drilling out. The orifice is the tiny pin-hole that is screwed into the casting facing the air-chamber. For close-up pics of the brass fitting and orifice keep clicking.

Here's a close-up of the regulator, spring and brass fitting.