Q:

Word for 'internal uniformity of an object'

I'm looking to convey the internal uniformity and indivisibility of an object.  
I like that monolithic means both 'uniform' and 'indivisible,' but I don't want to imply 'large size.'  
Homogeneity implies that the object is composed of other smaller objects. I don't want to do that either.

A:

I'm not sure I agree with your issue with homogeneity; some senses mean that the all the parts of the object are the same, others that there are no smaller parts (atomic, at least in the classical sense). For example homogeneous radiation has only one wavelength rather than a mix. Further, even if the senses that relate to parts suggest such uniformity that you can't meaningfully distinguish between them, so I would suggest homogeneous over your objections.
Monolithic likewise doesn't always suggest a large size, such as in monolithic kernels. I'd agree that it can in a lot of cases though.
Consonant is another possibility.
If it truly can't be split in any way, then atomic entails such consistency among the other traits.

