Outer: 2 1/2" wide (63.5mm)
https://www.amazon.ca/dp/B0BMBCQFD3?ref=ppx_yo2ov_dt_b_fed_asin_title
Universal galvanised steel U-bolts, inner width 85mm/3.34in, outer width 90mm/3.54in, which can hold up the luggage rack about 40mm/1.57 inches thick.
Inside: 3 1/4" Outside: 4"
Threaded Rod: