The van has metric fasteners. I like metric.
Thoughts on using metric 80/20 and plus-nuts for a camper van conversion?
Metric 80/20 extrusion and 80/20 part cost is the same as fractional. 25 mm = 1 inch, 40mm = 1.5 inch equivalent, that is, they are effectively the same size. Some of the slot sizes on fractional are actually sized to metric (i.e. 6 mm slot capability on 1 inch, 8mm on 1.5 inch). I found SS metric nuts and bolts to be up to twice the price and I am not sure all of the various choices were available. I am not sure about plusnuts in metric. Structure shapes (angles, flats) will be fractional in size (see http://www.onlinemetals.com
I did fractional after a bit of a debate. However, if you like metric as a standard, there is no overriding reason not to use metric.