These spacers are designed to prevent your weight plates from banging up against the mounting bolts on your plate storage pegs.
These fit typical storage pegs that measure 1.9" in diameter (slightly smaller than a barbell). This is the size used by Rogue Fitness.
This model will fit very loose on the REP Fitness storage horns, and will not fit at all on Titan Fitness products.
These will not fit over a barbell.
Be sure to measure your setup to see what size you need. If you need a size not listed, let me know and I can work with you.