These collars fit all GFRP/IRS small bore shocks (WILL NOT FIT CW SHOCKS) and allow you to run either a big bore spring or a small bore spring on the small bore shock with them. They are also larger diameter for easy turning. Running big bore springs on small bore shocks allows the car to absorb bumps and not feel as springy while still allowing the car to react quicker than a big bore shock due to the lower volume of oil. Big Bore spring bucket options- (57-1048 Raised, 57-1049 standard, or 57-1072 lowered buckets)