Mantua General HO Drive Shaft 4-4-0 ( Four Pack ) The General Model Train  12024
Hundreds have been sold

To have these made there was (CAD work, Proto Typing and 3D Monochrome Stereo-lithography (MSLAprinting  
I had to commit to many more than I needed. UPDATE ! (demand made me go back for more)
They are 3D Printed layer by layer at 50 Microns per layer. (Fun to Watch as it just appears out of the VAT of resin up side down !!!)

These are not factory parts but true replicas that function the same.

The Drive Shaft works just like the factory ones.(Same Size & Length)
Made with A Strong, Precise High Resolution 3D Printing Resin by Siraya Tech

From the Manufacturer 
Siraya Blu has excellent mechanical properties 
Tensile Strength 44 Mpa
Shore D 85
Young’s Modulus 1500Mpa
Elongation At Break: 25

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I have learned if you don't pick the train up properly they pop out and are easily lost. BUT!! you'll get 4 from me.

I offer these at a very low cost and shipping is included
You are purchasing just the drive shaft 4 pack