11 3/16 Between axle plates (inside measurement). If you looking at the rear view and notice the cross member... Measuring about an inch down from the member width is 9.5.
Looks similar to David Bird and TC Bros Brothers Hardtail Frames. The item "Weld On Rear Frame Section Hardtail 82-03 Harley Sportster Rigid Bobber 150 Tire" is in sale since Tuesday, October 14, 2014. This item is in the category "eBay Motors\Parts & Accessories\Motorcycle Parts\Body & Frame\Frames". The seller is "americanclassicmotors" and is located in Zieglerville, Pennsylvania.
This item can be shipped worldwide.