5/16-18 to 5/16-24 X 1-11/16. Mount exhaust to cylinder heads. Note: Exhaust studs as used in the M8 engine (OEM 10900015) is of a slightly different design, with a small protruding hex-shaped outer-end to aid initial stud-installation, but early style studs will still fit.
Fits: > 84-20 B.T.; 86-20 XL; 08-12(NU)XR1200; 87-10(NU)Buell XB