[Jon Stratis]

FYI... I was looking around on AndyMark's site to see if there was something we missed (like ordering incompatible encoders or something), and came across this page:
http://www.andymark.com/product-p/am-0174.htm

It includes this installation tip:

Installation tip:
If the encoder wheel slides loosely onto the 1/4" shaft, then follow this procedure to make the inside diameter of the encoder wheel collet to be slightly smaller:

Use a medium-sized pair of pliers and gently squeeze the collet portion of the encoder wheel. This is the longer protruding part of the encoder wheel with the parallel slits in the body. If you gently squeeze the sides together, equally, in 2 or 3 different locations, you can make the inside diameter of the encoder wheel slightly smaller. Then, the wheel will fit on the new shaft.

So, we're working on doing that now. I wanted to make sure to post it here incase anyone else has the same problem and comes across this thread!