US Digital E4P encoders and CIMple gear box

[swapnil94]

Your kit includes two E4P-360-250-D-H-D-B. These are miniature optical encoders with two-channel quadrature outputs. They are 360 codes per revolution and fit on a 0.25" shaft. See the E4P web page.

That is from http://www.usdigital.com/first
It says maximum shaft size is 1/4". But they are suppose to fit on CIMple gear box. now the output shaft of CIMple gear box, where encodere is attached is 3/8"
http://www.andymark.com/product-p/am-0740.htm

Diameter of small end: 0.374 inch

So how are they suppose to fit?
And if they do fit then they should fit directly on CIM's output shaft since the diameter of that shaft is 5/16" right? And are E4P able to keep up with 1:1 CIM full power?
Thanks