OEM Clutch springs tire after miles of heat and use.
EBC CK spring kits are 10% stiffer than standard and are sold in engine sets.
As stated in general fitting / safety instructions, you will find that the lever will feel slightly "heavier" when uprating springs, and that test rides are recommended to acquaint yourselves with this slight change in control.
Please Note: In some cases you may end up with 1 or 2 extra springs.
This is due to some bikes using the same springs but in different amounts.