A couple of comments with the aid of the diagram above so kindly provided by mg1polo.
As a new shooter, you will see references to a 2 hole target and a 3 hole target. In the old Winchester Western handset machines, you could set the width of the targets by placing a peg in a hole. If you put in the number 2 hole you would get about a 34 degree spread, 17° on either side of the centerline. If you put it in the 3 hole, you would get about a 45° spread, 22.5° on either side of the centerline . Nowadays it is common to set ATA targets at the 34° spread, however, it is permissible to set the targets at the 45° spread. Consequently, the target has to be outside of the 45° spread to be considered illegal. You can find references to these numbers up at the top of the fan in the diagram.
I installed 3 eighths inch rebar stakes at our club several years ago much like you have described in your original post. A 1/2 inch, 10 foot electrical conduit slides down on top of the rebar stakes. The stakes are set in concrete with the top of the concrete level with the surface of the shooting sidewalks. By sliding an electrical conduit on the center stake, it is easy to set the height of the target within the specifications without requiring someone to stand and hold a hoop.
To center the field, meaning to set the trap machine so that it throws equal angles to either side or doubles square to Post 3, conduits can be slipped over the 2, 17°angle stakes. It is then easy to visually ascertain if the field is set square.
We have G series Pat traps at our club and the width of the targets are governed by a 4 and 1/4 inch bar, or 34, 1 eighth inch increments, set between the 2 angle limit switches. Each 1 eighth inch of this bar represents one degree of 34 degree spread. While the angle switches can be locked in place with an Allen wrench, we have found it preferable to also tie the bar in place with a zip tie in case an angle switch works loose.
The most important thing to remember in shooting trap is that all dimensions are somewhat "about". Because of wind and changing temperatures and mechanical mechanisms the targets are going to come out about where they have been set. As such, as a new shooter, don't clutter your mind with worries about the fine points of how the targets are set, just bear down and shoot them where they are.
