absoluteBLACK Premium Oval chainrings for FSA ABS (asymmetric bolt spacing) cranks like Gossamer, SL-K, K-Force. This model fits all 4 and 5 bolt design cranks. 4&5 bolt cranks are identical except the one hidden bolt behind the crank arm in 5 bolt design which is not needed. These are finest FSA compatible chainrings on the market in terms of shifting, stiffness, smoothness of pedaling and manufacturing quality. 10/11/12spd compatible. Di2 Compatible.Size (Weight):34T (32g),36T (33g),38T (38g),39T (41g),50T (115g),52T (132g),53T (134g),.Compatibility: All FSA ABS (asymmetric bolt spacing) cranks like Gossamer, SL-K, K-Force, K-Force Light. Both 4 and 5 bolt versions. One model fits them all. Di2 Compatible. 10 / 11 / 12spd compatible. ABS cranks only.Material: cnc machined 7075 Txxx Aluminum. Long-lasting construction. Type II anodizing IMPORTANTFor Gossamer cranks - use original FSA bolts and spacers. There is nothing else needed to mount these ringsFor SL-K - use original FSA Bolt Covers and bolts that will fit perfectly. There is nothing else needed to mount these rignsFor K-Force - purchase additionally absoluteBLACK bolt covers. This is Absolutely necessary as you will not be able to mount these chainrings to K-Force otherwise.Ramps on big rings are specially configured for combinations: 50/34, 52/36, 52/38, 53/39TIf you wish to use other configuration it will also work, but shifting will be slower and may require more \"adjustments\" of front dérailleur to be acceptable. Also remember that front dérailleur can only accept max 16T difference between 2 chainrings - this is how Shimano and Sram designed them.