I misidentified (or misremembered, don't know which. Love this 7th decade) the machine we have as a Rockateer in the previous post. Not so.
Since it is a parts machine, I don't have a photo of it whole. Here is one I found from the internet
Here is a photo of the 500
So they look very similar and I called the 503 the Rockateer. I guess the 500 is the true Rockateer.
When discussing sewing machine repair, or any topic for that matter, nomenclature means a lot. I make an effort to identify parts by name. Not thingie or gizmo or whatitsname. So I wanted to clarify my mistake. This blog is meant to help folks figure out this wonderful world of vintage sewing machine repair and use. So I want it to be right.