Z1 900 & KZ900 Ignition Coils 4 ohm Coil, Cap, and Wire set… Sold as complete set. The distance between he studs is 3 1/2″ Designed for use as stock replacement – other coils or combination of coils that have at least 3 ohms primary resistance can be used. Since our coils are in the range of 4.1 OHM ,there should be no problem using our coils and the DYNA S Electronic Ignition. Replaces OEM# 21121-060 21121-058 21171-1019 21121-1003 21130-020 Fits: Z1 (Z1) (1973) Z1-A (Z1) (1974) Z1-B (Z1) (1975) KZ900-A4 (1976) KZ900-B1 (LTD) (1976) KZ900-A5 (1977) KZ1000 (1977) KZ1000 (1978) This set will fit many other models between 1973 -80 Besides z1900. Distance between the mounting studs is 3 1/2 inches.