Cargo box mounted on flush aero bars using T-slot bolts

Does anyone know the best place to source T-slot nuts and bolts to mount things to racks with T-slots? Might also want to look at thule t-rack

Feature: 1) 100% new and high quality 2) Easy installation 3) High hardness, wear and corrosion resistance 4) Compatible with most track systems

thule frameklem met slot Then when you don't need them, pull them out until you do For work or play, getting down to business, or heading out on Safari

thule slot vervangen T bolts have 20mm x 20mm square plates which fit into the Thule track I have BMW roof bars and the track groove is larger so I need the Thule T