Thanks for the photo, Bob. It works here too. You put the forward slash after the G instead of before the I.
I edited your photo
I see how it clamps around the boom, but I don't understand yet how the angle can be adjusted.
Are the adjustment holes under the clamping plate or in it? How many degrees between each setting?
Do you need to move two bolts, or just rotate the plate with the bottom bolt as a pivot?