[Dan Case]

Seller's on ebay® typically call them 2-1/4" or 2-5/8" but these are not actual measurements. The inner diameter of the threads is close to one of these tape measure sizes for their purposes. The average thread outer diameters I measure on 1960s Cobra hubs and axles are right at 59.25 mm which is about 2.33 something inches.

If I am not mistaken all SAI cars in the 1960s used the small size threads with one of several different taper sizes. (Check out period pictures of leaf spring competition cars, especially independently prepared and campaigned ones. I use to see racers with KOs on hubs or axles by only two or three threads. It was common to see the end of the hub or axle only partially “in” the KO. One letter in an old club publication indicated the writer bought a car with the rear KOs only engaged 1-1/4 turns and the writer wanted to know what to do improve safety.)

I have found genuine pre-1970s NOS KOs from Halibrand with two distinctly different size tapers. The “small taper” will not work on my car and its 1964 vintage wheels as the arms of the KO bottom out on the wheel prior to the taper making contact with the tapered seat in the wheel. The “large” size fits just right. Evidence suggests Halibrand KOs were made (It is believed that the aluminum ones were not actually made by Halibrand Engineering.) with a succession of different forging dies, for one thing the “ears” changed width, thickness, angle, and shape over the years.

The people selling the large thread size usually say they came from or are for sprint cars. Some sellers don’t know the difference. I have purchased some sight unseen that were advertised as being the small size but turned out to be the big ones.