Looking to BUY Athearn Blue Box coupling and spline. Spline is about 5/8" long like photo. Thanks.
http://www.athearn.com/Products/Default.aspx?ProdID=ATH34128
The upgraded worm gear assembly, made of delrin for quieter operation.
The OP has the “universal” type fitting on the worm gear shaft, with the spline drive shaft.
The newer assembly has a “dog bone” type fitting, and the drive shaft has a hex head into the fly wheel, and the “dog bone” on the worm gear end. Athearn calls it a female coupling.
Doesn’t look like Athearn has those anymore.
You should be able to find them on Ebay.
How many do you need?
Mike.