This is fairly accurate 15-ton Federal axle used by first two Grave Diggers.
Blog post about Grave Digger’s axles:
https://www.artstation.com/jorma_rysky/blog/L8Ry/1961-15-ton-federal-axle
Sources for information:
http://monsterphoto.iwarp.com/den2a.htm
http://monsterphoto.iwarp.com/den2.htm
I do not own name Grave Digger, nor I’m anyway affiliated with Feld Motorsports. These axles are generic axles by Federal, and my model does not have any copyrighted stuff, all the logos and markings are removed/were never there.
Additional files includes Blender and Substance Painter-projects, and all the textures before baking them together with Simple Bake. Main colour of axle is adjustable in Blender.