ANSCS3009 Answer-RC RC8 Clutch springs x 3pcs 0.9mm 3pcs.

Answer-RC RC8 0.9mm 3 Shoe Clutch Spring Set 0.9mm Gold.

A lighter spring allows the clutch to engange earlier with more progeression.

A thicker spring allows the engine to rev higher prior to engagement of the shoe coming in with more bite and more aggression.

If driving on a low grip surface it is generally considered best to run a lighter spring making the car easier to drive out the corners.