This set has four of each: Convertible Knobs, 1-1/2'' MightyBolts, Track Nuts, 1-1/4'' Socket Head Cap Screws. All standard 1/4-20 thread. It's compatible with YakAttack MightyMount’s, GearTrac, and most other kayak track systems from Scotty Fishing Products, RAM Mounts, and YakGear.