Pensker
Your metal frame is probably constructed with 3/4" EMT (electrical mechanical tubing), otherwise known as electrical conduit. There are several dedicated connector designs available, but when designing and building my frame last year, I used FrameMakerClamps. You might get some clues as to how your frame goes together, by checking out the details on this website (I'm not affiliated in any way, other than being a happy customer) -
http://www.framemakerclamps.com/
If you click on
Examples, then click
Page 1, you will be directed to photos I had taken of my boat and frame. Hopefully this will be enough for you to figure it out.