These are the standard studs that use an inner nut to fasten them to the engine case. (see pictures) They fit cases from 1912 to 1920 that were not threaded.
Fits All 1912 - 1920 Singles & Twins
Includes:
Chain Guard Stud 472-12
Inside Case Nut BO759 1/4" - 24 TPI
Outside Case Nut 472-15 5/64" - 32 TPI
Includes 2 Studs, 2 Outside Nuts, and 2 Inside Nuts.
** After these are installed on your case, the inside threads should be spiked/mushroomed to insure the inside nuts will not come loose in the motor.