Two of these fit together in the truck roof accessory port. Tested for compatibility with Rivian R1T (2022). Threaded holes for M10 or 3/8th bolts. Should be used with a bracket such as the "2-Hole Flat Straight Strut Fitting Bracket" sold at hardware stores.With four of these (plus 4 M10 or 3/8th bolts, nuts, and 2 brackets), you can mount strut across the ports of the truck roof to fashion DIY crossbars for well below OEM crossbar prices.Similar to the truckbed port adapter here, only this one is for the roof accessory ports.