Those straps will be in the same section, and made by the same manufacturer, as angle brackets. Get nuts & bolts to fit. In the past I've squared off the whole the bolt goes through to use a carriage bolt just so I only have one side to worry about, but that is adding unnecessary steps as it doesn't have to be very tight. Like Robert said, use wing nuts on the top.
@Robertfishes,
Is that ply screwed together with drywall screws to build up to width? How well is it holding up for you? Is there any glue in there too?