This are replacement gear boxes for vintage Joe Works straight boiler Shays.
They allow all wheel pickup due to isolated frame work and proper allignement of the gears. Note, that on one truck, the whole in the front to hold the worm gear shaft as 1mm in diameter, while the other one has 1.5mm. This is the configuration as it was on my Shay and I'm not sure if this is common to all other Shays.
Attention!!! This replacment trucks may not fit the later build T-boiler Shays as they use a different design!!!
More about the replacement parts and how to install them is shown on my blog.
There's a Video of the finished Shay with the new gear boxes at YouTube